Krell FPB 300cx vs Jeff Rowland 501's?

That Rowland, a classic ICe amp without an analog power supply, will be dependent upon quality of the A/C power supply, while the big 'ole Krell, with its beefy analog power supplies, will be much less so.

The Krell is probably 400-425 watts/channel into 8 Ohms, the Rowland roughly 500. That's not going to get you any practical increase in headroom over the Krell (doubling wattage yields only a 3 db. increase in output).

You would likely have greater midrange clarity with the Rowland, which is an ICe amp module characteristic, but you would trade high frequency purity, which is an ICe amp module weak point that shows up in the Rowland 201/501 implementation.

The Rowland is of course much more energy efficient, if energy bills are an issue for you.

In short, while I have not heard either amp on your speakers, my guess is that you would merely be swapping flavors. If additional power is your goal, I would buy a much more efficient speaker that plays big (e.g., WattPuppy 6, 7 or 8, or Escalante Fremonts), as you really need to spend a lot of money for amps that will give you a significant increase in headroom over what you have. PS - I have nothing against Rowland equipment - I have run a Rowland preamp for nearly six years and used to own Rowland amps.

The Rowland preamps are very quiet, which is a crucial performance parameter, and especially quiet when run with balanced equipment. As Guido notes, they also feature a very low output impedence, meaning they can drive anything (I was able to drive my darTZeel amp with a 50 Ohm BNC connection - my Coherence II has a 50 Ohm output impedence - but ultimately decided on a balanced connection). Finally, the ones I have personal experience with layer space and have the musicality of the best tubed preamps (which says a lot). In short, a Rowland preamp will always be competitive with the best solid-state preamps and would presumably work nicely with the Krell.

The Capri is no doubt a nice linestage and I again note that I have been running a Coherence II for nearly six years and owned Model 6 amps for several years - I really like Rowland equipment - but even accounting for obvious synergy between the Capri and the 312 amp, I have a tough time accepting that the Capri bests the ARC Reference 3, which is one of the small handful of very best line stages, in each of the following areas: "greater top to bottom extension, linearity, harmonic complexity, authority, macro and micro dynamics". With all due respect, that doesn't sound right.