I’ve been watching a number of your videos where you talk about recording in DSD, converting to DXD and then outputting 1-bit SDM.
Have you tried HQPlayer’s “Pro” version? This is exactly what it does:
Grammy Award winning mastering engineer Tom Caulfield has made stacks of NativeDSD.com albums using this.
Together with Pyramix, as you mentioned too.
There are a number of HQPlayer users on your forum here, including myself.
The Pro version is made for mastering engineers or those that want to create offline files. I have no need for the pro version - it’s too expensive for me. I just use regular HQPlayer for ‘on the fly’ conversion.
I think the solution you are trying to develop with this Zephir thing, already exists!
Use HQPlayer Pro to go from DSD to DXD. Mix in Pyramix. Then output 1-bit SDM. There are a gazillion filters to choose from in HQPlayer (minimum phase, linear phase, intermediate phase).