Hi. I'm after some advice.

I have an RME ADI-2 Pro FS R BE, it's connected to my computer via USB, used as an audio interface/headphone amplifier. I use it with a set of HIFIMAN Arya V3 headphones. I also have a guitar setup going out through a UA OX, coming in via S/PDIF.

I would like to be able to directly monitor my guitar output and what's playing at the same time with minimal latency. This is so that I can have a play along to backing music and listen both the guitar and the backing track with my headphones. The RME supports S/PDIF, but AFAIK it doesn't allow playback at the same time. It's one or the other, right?

A while back, I could do this just fine with a Roland UA-55 Quad Capture (fairly old now) as it provided a direct monitor, so that I could hear playback+S/PDIF. There was no noticible latency and I could even control the mix between playback and S/PDIF. However, this device doesn't come close to the RME, there's a large and noticible difference in sound quality between that and the Quad Capture (it's not just me, other people have commented on it blindly).

TLDR; how can I get the best sound from my Arya headphones using my RME ADI-2 Pro FS R BE while being able to directly monitor playback and a seperate S/PDIF line (ideally being able to control the mix that I hear between the two & record both sources). I love my RME ADI-2 Pro!

I don't mind if I have to spend money on a mixer set up of some sort. Ideally I don't want to spend more than a couple of thousand dollars (I prefer not to do it in a DAW), but I want to get something professional that will last a long time. The RME and Ox are already expensive peices of equipment. Also, I want to be able to record playback and S/PDIF together.

It sounds like TotalMix might give me what I want and I would be very happy if someone could point me towards a solution that uses this!

Help! Please!

Thanks.