I've compared the internal DD/DTS decoding of my Pioneer 757i with my Tag AV32R (BP-192) and, as you would expect, the Tag is leagues ahead. The Pioneer isn't bad though and I guess would compare with some budget AV amps perhaps.
The Copland (and I assume you're talking about the CVA306 6 channel valve pre amp) is a lovely bit of gear. Although you have to rely on the DVD player for DD/DTS decoding and cannot of course apply an processing to analogue sources (DPLII to TV etc) the flip side is an outstanding 6 channel pre amp that should be superb for DVD-A/SACD.
It might be worth trying out the Pioneer if this is possible and also comparing it to the likes of Denon's 2900 and maybe Sony's 999ES (the Sony doesn't do DVD-A mind).
Finally, I presume you won't be using the Pioneer for CD replay as again, it's not bad, but a dedicated CD player would be a lot better, especially with a quality pre/power amp like the Copland.
Matt.