I find for my setup, lifting all grounds in the inputs and outputs but leaving the shell grounded gives the best sound. The other way around, lifting the shell and leaving the outputs grounded is slightly brighter. Leaving the output and shell grounded gives a slightly dirtier duller sound, but lifting all the grounds including the shell is a bit on the bright side in my case. I am using all inputs except the XLR’s on my MK2.
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I waited until I had over 400 hours on my Mk2 and yesterday I lifted the grounds on all inputs (I am only using USB and optical) and felt that I had found a nice improvement in transparency and bass depth and slam.
I will listen to it this way for a few more days and maybe switch back. I haven’t messed with the balanced outputs yet.
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I checked my setting after one week of vacation. Mine is similar with the exception that I only lifted both I2S inputs (using both) and grounded other inputs (not in use). I prefer lifting outputs but grounding shell too. I also had a USB shorting plug in, but I forgot if I liked it or not. One week is quite a while ago 
Frankly I am not sure this would be my final setup and I was still experiencing. This seems to be the one I kept going back to, so it is close. I will need to wait for two days because the system is stone cold and sounding dull now.
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After my vacation, my taste of ground setting has changed. Now I like lifting all inputs, and outputs, but keep shell grounded. Also, this setup needs the USB shorting plug to work its best. Somehow the system with this setup sounds a lot better than my previous setup.
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If you use the USB input you won’t have to use the shorting plug. 
In my setup, I lifted the inputs and could not perceive a difference in lifting the outputs.
I suspect each system will have its own synergies, and there won’t be much in the way of a standard on these settings.
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You’re right. My next streamer will have a USB output, and we maybe still waiting for AirLens.
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I thought your Summus 2 had USB outputs
For the past week I have been listening with nothing lifted. Tomorrow I am going to start a week with everything lifted.
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There are four USB ports, and they are all inputs strangely. I have a nice USB cable sitting in the drawer now.
I lifted input as music played and heard a difference as I was lifting. When I lifted the output, I did not hear any difference, so I returned it to grounded.
I am using RCA connections. Not surprisingly, the shell lift had no audible effect.
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You need to reach out to them as according to their literature every one of the Summus configurations has USB output capable of DSD 512.
It’s a shame we can’t do this with the remote.
I agree.
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Maybe there was something I didn’t know. I couldn’t find one USB port that worked. I’ll dig into it tomorrow. Thanks!
I would reach out to Arthur at Power Holdings or even Al since he’s had one for some time. I can see the ones on the front maybe being inputs but the ones on the back should be outputs. Maybe something in the software setup. There was also a group of users on AS at one time.
I reached out to Robert who is the Euphony guy I have talked to in the past. Hopefully I will hear from him soon.
Maybe the USB cable is bad?
That’s possible. I’ll try it later since I was told all USBs are inputs and outputs on Summus.
@dawkinsj, thank you for pointing me in the right direction. When I first tried USB, I did not disconnect I2S. I also did a power recycling on Summus2. This time I got a green light, and MK2 shows DSD256 file is working.
But I could not turn on the entire system yet since it is too early in CA. @vmax, the USB cable works, and I can finally compare the two connections!
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