Krell FPB 300cx vs Jeff Rowland 501's?

I am thinking about making this change. Has anyone compared these two amps? I have B&W 802N speakers which love power.
I have been very pleased with the Krell power and the sound of the cx version of the FPB.
JRDG 501's are rated at more power, are monoblocks, and quite a bit smaller, but are class D. Is this a step up or not?
FWIW, soundwise, I'm thinking its more a lateral move albeit an energy efficient one with a bit more power.

Might open up dynamics a bit and go a bit louder.

I'd expect the Rowland to be a bit smoother though if the current setup has an edge to it.

I think Krell/B&W is a good match off the cuff though.
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 JRDG 501 are undoubtedly very fine amps to start with. . . loads of controlled power to drive any load and a very open and easy to listen sound. For the reasons explained by Raquel above, if you want the ultimate out of the 501 monos, you need to add to them a pair of external JRDG PC1 active Power Factor Correction (PFC) units. These devices preconvert the AC from the mains to a steady 384V DC current fed into the monos through a banck of intermediate charge capacitors and make the 501 much less sensitive to AC noise and fluctuations. They also keep the 501s internal caps optimilly charged avoiding AC induced ripples. PC1s should yield even larger authority to the 501s and will give them a lot more subtlety and nuance. It is said that the PC1s let the 501s approach the performance of the JRDG 312 stereo flagship, which is my very fav amp of record. The PC1 is not on the website yet. Your dealer can order them for you. They list for $1500 each.
I wish I could answer your question more completely and directly. Unfortunately I can't compare the 501s with your Krell, as I have no direct experience with the FPB 300cx . Guido
Thank you all for some great information. It is very helpful. Maybe I should keep the Krell (Raquel, I have a 30 amp dedicated AC line that seems to serve the amp very well).
Maybe, I should ask a follow up question regarding the Krell... How does a Krell FPB 300cx mate with a Jeff Rowland Pre... like the Capri, for example? I would run it balanced.
Chances are the Krell will mate very well with Capri, as Capri has very low output impedance: the manual lists 40 Ohms single ended and 80 Ohms balanced, making it quite compatible with most amps on the market. Other Capri specs and manual at:
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.
I even prefer the JRDG Capri to my ARC Ref 3 for driving my JRDG 312 amp. To my ears, Capri yields greater top to bottom extension, linearity, harmonic complexity, authority, macro and micro dynamics. Staging and imaging seem to me comparable between the two.
Wow! That is quite a statement that you prefer the capri to the ARC Ref 3 considering the Capri is about $5,000 cheaper on the used market. Was your preference given with or without the Rowland A.C. filter?
My preference is for the Capri directly plugged into the AC, without PC1 Power Factor Correction device. I am planning to test the PC1 on Capri once again in the near future. I have tried 3 PCs on Capri this far:

PAD anniversary -- oddly, I did not like it in this application. . . some unwanted warmth in the lower part of the spectrum, slightly unclear bass, and a feeling of harmonics in the treble region 'disconnected' from the fundamental. Pad Anniv works very well on my X-01 Ltd and on ARC Ref 3 instead.

Cardas Golden Ref -- Good wire without too many flaws. . . not the ultimate extension, and some very slight raggedness at the top.

Shunyata Anaconda helix Alpha -- My preferred PC of the group. . . The most extended and apparently linear. One criticism that has been made by some to Anaconda is to yield slightly softened transients. . . but I still enjoy it very much.

Hope this helps. Guido
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.
Raquel, you are correct, outwardly at least, my preference does not sound terribly credible--the Ref 3 retailing for almost 4X the Capri, being rather diminutive, and internally rather sparsely populated. On the other hand having lost my eyesight 25 years ago, I am not particularly sensitive to the alure of component size, parts count, or striking cosmetics. . . I just let my ears 'do the walking', and more often than not, the 'surprising'.

It is worth pointing out that, in the post you refer, I did not use the term 'best' because it is suggestive of absolute valuations that I personally abhor. . . rather, I said "To my ears, Capri yields greater. . ." What I heard is neither right nor it is wrong. . . but simply my final preference of a comparison which lasted a month and a half in my own system, and admittedly started with a great deal of skepticism from my part. Initially, the Capri being factory fresh, my over 3-year old Ref 3 appeared to yield easily greater refinement, but past the 300 hrs breakin mark, my preference started to shift towards Capri, and firmed up during the subsequent few hundred hours. Approximately 3 months afterward, I put back the Ref 3 into the system for 3 weeks and swapped pres back and forth a few times just to determine if I had suffered temporary delusion. . . even inserted 6H30DRs for the occasion and a fresh SED Winged 6550C. In the end I threw in the towel and I reverted back to Capri. I concluded that either I had not suffered of delusions, or that my delusion was of a more long lasting/grievous nature, because I still easily preferred Capri.

For what it is worth, While I remain uncomfortable at the very word 'best', Rowland has commented several times that Capri is the best sounding Pre he ever created short of Criterion. He attributes a lot of its sound to the Texas Instruments Burr Brown OPA1632 differentially balanced quasi op-amp that he used at Capri's core.

All evaluation was conducted in balanced mode using AudioQuest Sky ICs. For PCs I tried Cardas Golden Ref, Shunyata Anaconda Alpha Helix, and PAD Anniversary.

I Hope this illuminates my experiences with these devices.