Preamp DAC option.

Everything depends on how it sounds with the other coponents in your system including cables. It will help everyone here if you list everything else.
The Bryston tends to be dry sounding so it is a good match with a system that is dull or closed in sounding but if your system is already detailed with fast tight bass you might want to try a few different pre-amps.

My system consists of Adcom GCD600, Pioneer DV578AS, Adcom GTP400, Bryston 3BST, Mirage M7si. I'm looking into both the BP6 and Conrad Johnson PV14LS2.
My understanding is that the DAC option on the BP6 would allow my preamp to do the conversion rather than my GCD600 or Pioneer.

Hello again. You do not want to do the Bryston with that system. Everything you have put together has a metalic glare in the top end that causes everything to have way to much sparkle. You need to find a tube pre-amp and don't worry about the D/A right now. The D/A will make a much smaller difference in your system than getting a very smooth pre-amp. Try to find a used Musical Design, VTL, Quick Silver, TerraSong, or Encore.

Hello Duane. I'm also looking in tube pre-amps. How does the Conrad Johnson 14LS2 compare to the units you listed above?

Hello again. The CJ is not bad at all but tends to have a sound all it's own that can be overly intusive once you get tired of it. I will say that Bill Conrad is a very honest buisness man and you will find long term service if you buy it. The others I mentioned I would give the edge to when it comes to being way better than the price tag suggests. The 2 that really stand out for that are the Musical Design and the Encore. The Encore is the best of the 2 but sells used for twice the price.