Bob,
Yes, the S1 is replacing both the ARC DAC8 and the Bryston BDP-2. I'll be putting both for sale here tomorrow.
Differences in sound are definitely there. Sometimes is hard to tell differences with DACs but in this case is not as subtle. The DAC8 traditionally has excelled in the bottom end and, in my view, it has a deeper bottom than the S1; however, the S1 has a tighter bottom. Where the S1 stands out is in the top and middle ranges. I was talking with Mark earlier today, I'm hearing detail and information, from music I know very well, that I've never heard before. The stage and instrument separation is fantastic. And, the interface is second to none. Finally, I just simplified my system and rack - less components and cables.
The Bryston and ARC pieces are very nice and someone will be a very happy owner.
Hope that helps Bob. Still breaking in the Lumin. Maybe Bud will comment as well. He received his S1 today.
Cheers!