Any of the Musical Paradise MP-D2 versions as the mod deals with the parts in the power supply and regulation circuits plus biasing.
Musical Paradise D2 DSD DAC Mods: $500
RE-Bias tube stage for optimum operation (for tube type) and upgrade signal path resistors.
Revised high voltage to be compatible with new tube operating point.
Add MWI high quality bypass caps to B+ supply - none present in stock unit.
Install MWI's own Solid State High Voltage Regulator (SSHVR) circuit for tightly regulated high voltage supply to tube plates.
The result is a huge improvement in sonics. Tighter and more controlled bass. Lower distortion, bigger and better soundstage as well as focus. Overall tonal balance is more natural and accurate, while still providing the beauty of tubes.
Never heard the BP DAC only know what Joe told me about it. I think due to the price difference new the Aqua is probably built to a higher level to start with. For tube DACs I have had the MP and the Line Magnetics which is also very good sounding in it's tube mode. SS mode not so much. As I am not interested in DSD I don't really have much interest in the newest MP version as that is where the improvements are. I may have Dan do the mod on my Mk I version though.