Hey,
Is there a dac/headphone amp combo or just a dac available with 2 USB inputs?
At least with two imputs that could come from a Mac motherboard that has no RCA out, cause I thought of using the Schiit SYS with adapters to standard TRS but that seems scuffed.
It is for a desk setup with two computers and preferably one set of headphones.
Thanks 
Never see a Dac with two Usb in.
What you can do is buy a Dac with Usb,Coax and Optical in.
One Pc connect with Usb and the Other Pc coax or Optical.
I mean Optical is better because the humms from the Coax.
Maybe when your Pc has no Soundcard you must buy one who have Optical or Coax input on it.
What I do currently is run usb from my pc and optical from a hub to my MacBook. Works well. If needed I could also adapt another input to the coax spidf input.
Do the (presumably) @ZeosPantera approved method, blue tack two SMSL Su-8’s together, manually power one one and leave the other off, use the remote to power it off and the other one on with one press, leave both on USB input so it toggles between the two. Use an RCA combiner (reverse Y cable basically) to output to one amp.
You could in theory use any DAC with remote that uses IR for control.
I have USB running from my computer to a Schiit Eitr (converts to coax) then to the DAC. My iPhone is plugged into the USB on the DAC. That seemed the easiest way for me to get 2 USB’s into the DAC.
Still thinking about this. I see the Zeos review of the MOTU M2 2x2 USB-C Audio Interface.
It says 2-in/2-out, so if I used two 1/4 inch to XLR cables, each going from their respective computer input to the M2, would that allow me to hear the two in the one headphone out?
come to think of it, those are combo jacks on the front. So I could just use 1/4 inch cables
While that would work, you would have to set levels per channel (L and R). Easier would be a Yamaha AG03 or similar.
One source hooks in via USB, the other via line level.
Headphone port is on the device, a headset-mic could also be hooked up and feed to the computer connected via USB.
I’ve been looking for exactly this.
I really only found one, and its more on the lower end, but perfect for me. DAC Amp (low power).
Two USBC system inputs, one 3.5 headphone jack, a 3.5 line in and a line out. The line out is unpowered (for speaker connection).