Actually, the subs are the same make, HSU. However, they are different models. Guess I’ll check in with the HSU folks and elsewhere about the best hookup.
In any case, I will probably order the Stellar DAC/S300 combo tomorrow and give it a shot! Worth it to go for a 30 day trial. Should be interesting…
Thanks again for all your patient help. I really appreciate it!
John
So, after gathering some other information, ran across the concept of daisy-chaining the subs. One my subs has high-level inputs and outputs. So, my plan is to tap off of the S300 to feed sub 1 with the outputs, and then daisy chain to sub 2. Definitely negates my current capability to base manage each sub individually, but I’ll just have to manage that manually. Hopefully that won’t be too difficult.
BTW, placed the order for the SGCD/S300 combo and just awaiting the notice of shipment! Eagerly anticipating…
Just thought I would do a follow-up. Received the SGCD and S300 and have incorporated them into my system. Everything seems to be working fine. For HT, the Denon handles all speakers except the fronts and subs, which are handled by the SGCD/S300. Indeed, lost the ability to base manage the subs thru Audessey, but manual control seems to be working so far. Then for 2 channel listening, the SGCD/S300 handle the fronts and subs, (driven from the line level outputs of the S300), and sound great. Still in the process of breaking them in, so I hope they sound even better as time rolls on. So far, glad I took the leap!
Does your SGCD’s HT Passthrough work OK? I got a loud pop/thump when switching to/from HT pass through input from another input like spdif/USB/I2S. PS Audio confirmed the problem, but ignores. It’s been like 6 months now.
https://forum.psaudio.com/t/new-sgcd-loud-pop-thump-when-changing-to-from-ht-input/5969
The Home Theater passthru seems to work fine. I too get a pop when switching to it and I know I saw a reference to this from PSA somewhere and they commented that it would not damage the speakers. Seems that may depend on how loud the volume is turned up. For the life of me I just can’t find that reference now.
Yes it won’t damage the speakers but it’s quite loud and really annoying. In my setup the volume does not matter, always got a loud pop so I have been switching cables manually. I’m planning to build a input selector box triggered by AVR’s 12V trigger. I have had many name brand amps with HT pass through feature and non of them had this pop, only silent relay click but unfortunately SGCD does not have input relays and that’s why it has input crosstalk also - sadly I did not know this when I bought it. So as a pre-amp it’s a piece of crap but as a dac it’s great for the money IMHO. To my ears it sounds better than my Mytek Brooklyn.
As I mentioned, I do get the pop, quite noticeable but not annoyingly loud. I have the HT passthru volume set to 76, which the users manual says is line level value.
Exactly level 76. I have big tower speakers with M700 monoblocks maybe that’s why I got so much louder pop - almost feel it in my chest, really!
BTW, I just got good news from PS Audio customer support that this problem has been solved with new firmware update so contact Jeremy. 
The users manual says that the SGCD firmware is not field upgradable. So how would we get any update?
With new PIC chip. You have to send your SGCD to dealer or if you are capable you can DIY. Actually it’s really simple, just pull the old one out and push new in but you definitely have to use antistatic wrist strap. Without the strap you could damage the chip.
Yeah, got that information from Jeremy last evening after I contacted him. I will probably go ahead and do that myself if necessary. He is checking on my firmware version now and will let me know if there is a more recent version available.
So, thought I would come back with an update to my system and a plan to get back to Audessey control of the subs for HT. As described above, I use the SGCD/S300 combo to power the front L/R and both subs, however without Audessey control of the subs. In reading a thread elsewhere I came upon a possible solution utilizing an RCA switch box. I would connect the RCA output of the S300 to one of the RCA inputs on the switch box. Then, the RCA outs of the switch box would go the high level inputs of the subs, one channel to one sub, and the other to the other sub.The sub-outs of the Denon 4300, which would only be turned on for HT, would go directly to the LFE inputs on the subs. Thus, when I want to listen to stereo only, I would switch to the input on the box from the S300, and for HT, switch the box to an unused input, thus cutting out the input from the S300, and turn on the Denon so the sub-outs then input to the subs. Also, the RCA box has a remote, so I can incorporate control into my Logitec Harmony Elite universal remote to switch the box to the proper input remotely.
Would love to hear any constructive comments about this plan of mine… 
Have this system up and running now and all seems to be working well. Only difference is that when I listen to HT I actually turn the switching box off, thus cutting off the high level signal to the subs. Only minor flaw is that I leave the sub crossovers activated for both kinds of listening. Therefore, both the Denon Audessey correction and the sub crossovers are applied for HT listening. I could get up and turn the sub crossovers off, but that is probably not going to happen. Since I ran the Audessey correction with the sub crossovers on, hopefully I’ll get the proper end result. Still doing some listening evaluation, but so far it appears to be working as I had hoped.
I finished my input selector boxes and the switching is done by AV receiver’s 12V trigger. When AV receiver turns on then relays switch inputs to AV receiver - one box for sub (RCA) and one box for fronts (XLR).
I also installed miniDSP for the sub with really great results. I’m thinking another miniDSP between player and dac.
Nice! A bit more sophisticated than mine. The RCA switching box I settled on is the one below. As I said above, because it has remote control, all I have to do is say “Alexa, turn on stereo music” (whichever input I want) and the AVR is turned off, if it was on, and the PS audio and the switching box are turned on to the proper input. For HT, I just say “Alexa Turn on HT” and the AVR and all of the proper HT components are turned on, with the RCA box left off. Seems to work so far. What exactly does the MiniDSP do in your setup? I’m not familiar with that.
Thanks! I use miniDSP’s PEQ to reduce the subwoofer’s peaks (bass/room boominess). The bass is so much better/cleaner. You can read more here: https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd
The second DSP I’m considering for floorstanders is this one: https://www.minidsp.com/products/minidspkits/minisharc-kit
I’m planning to install it between Raspberry pi and SGCD using I2S signal.
