I run my Nautilus 801's with a Wadia 860 directly into an FPB600c... I feel as though Mark Levinson's latest amps including the 33h's can not supply enough bottom end compared to the latest Krell gear... I have not heard the digital amp from spectron. I have heard the digital amp from Tact at HI-FI 99. I thought their system was extreemely thin sounding. But that was that particular system only! I have not A-B compared any Krell FPB's directly to the latest Mark Levinson's. Although, I heard in various systems using most of the Levinson gear up through the Reference. Good stuff but not enough sound quality for the dollar compared to the Krell FPB's. If you pay very close attention to the quality of your incomming power the Krell's will sound better. They are super-transparent as are the Nautilus 801 & 802's. Your budget will dictate how much performance you can get.