The best ADCOM preamps in order of excellence are: GFP-750,GFP-565, GFP-555II, GFP-345(with PHO-802A Option), GTP-400, GTP-500II. Some of the Parasounds are pretty good too. but I am not as familiar with their design. Make sure you get the ADCOM 555II and 500II versions not the ealier versions which are not as good.