A buddy of mine had both and his comment on the dac within the BP26 was "It has this sound which I would describe as "more detail but hollow and less substance". I am not 100% sure but I think the DAC in the preamp may be a single chip (CS43122) as opposed to a fully balanced dual chip set in the BDA-1 which are CS4398, same chip that is in the BCD-1 but as I note I am not sure.
I have a BDA-1 on hand right now and it is impressive even with a not too fancy optical nor a very good coax cable in play.