Bryston BDA-1

I think this is the warmest, most well rounded DAC I have owned, and I have had a bunch of them (7) in the last year.

I don't believe that there is any breakin period for a DAC, what would need to break in?

It may just not be a match with your other gear, or it could be the cable. I had an MHDT Havana that we excellent, and very warm as an alternative.

Apparently Bryston burn their gear in before shipping out; or so my local salesman told me. I had one for trial and came to the same conclusion as you and sent it back disappointed. Could be an issue of synergy with with my gear but nonetheless was underwhelmed to say the least. For the same price I bought a Droplet 5.0 with a factory fitted digital input that provides a better experience than the Bryston

I cannot comment on the Bryson as I have not heard. Obviously, transport, cables, PC, line conditioners and music format and interface (coax, usb, toslink) should/could make a difference. When you say you don't have the 75 ohm cable, do you mean you're using a standard RCA IC? Are using USB? That (USB) would be the poorest interface (and does not support hi rez). I would at least try a digital cable before returning it.