I have owned many Krell amps (have 2 now) including the FPB series.
A passive preamp would technically work fine, but in my experience they perform best with Krell active preamps. With the "C" versions, if you can use it, it would be best to use a cast preamp. In my system, since I have the KBX active crossover, I can't use cast, so I use the KRC-HR. When I remove the preamp from the signal path and drove it directly, the sound was NOT as good.
Richard
A passive preamp would technically work fine, but in my experience they perform best with Krell active preamps. With the "C" versions, if you can use it, it would be best to use a cast preamp. In my system, since I have the KBX active crossover, I can't use cast, so I use the KRC-HR. When I remove the preamp from the signal path and drove it directly, the sound was NOT as good.
Richard