Musical Fidelity 550K/750K Supercharger?

I'd like to know if anyone has any experience with the Musical Fidelity 550K or 750K Supercharger power amplifiers. I am presently using the Rogue Audio M-150 tubed monoblock amplifiers, whose sound I'm very happy with, driving B&W 805s in a medium sized 15'X16'X8' high, acoustically treated (ASC Tube Traps, Echo Busters) basement room. Although I have read Stereophile's very positive review on the 550Ks (increased dynamic range with no alteration to the donor power amplifier's sound), I am interested in hearing from any users of this product(s).

My musical tastes run from rock, thru jazz, with the occasional classical selection thrown in. Listening levels at the listening position (approximately 7' from the speakers) are about 85db SPL (average,C weighted, measured with my Radio Shack sound level meter), but occasionally I will play louder. I use my 805s with a Velodyne sub, whose signal comes from the Velodyne SMS-1.

Any input/feedback (no pun!!) would be greatly appreciated!!