Aragon D2A...I like it...sorta...

I own and enjoy several pieces of Aragon equipment. Recently, I just picked up an old D2A (not the MkII) converter. I hooked it up to my 24K preamp and found that it greatly increased the transperancy and detail in the midrange and highs. However, there was a simultaneous effect on the bass as well and I found that it made the bass much more muddy than running directly from my Cd player. I'm not talking less strong, but clearly less controlled and looser than running directly from CD. Muddy is the word. Now I'm aware that this unit was superceded by the Mk II unit. I was wondering if the changes in the unit were significant or whether it was simply a matter of changing out power supplies. Is it possible to still get an upgrade on this unit or it's power supply? If not, can you suggest how I might clean up the bass response? My associated equipment is a Nak CD4 (used as transport), Aragon 24K preamp, Dynaco St-70 amp, Audioquest Midnight cables (biwire), and Vandersteen 2ces. Don't tell me that my amp isn't good enough, I've heard much better bass out of this baby. Todd