Don't sell the AV-405, unless you just want more power. No surprise that you find it sounds better than the bridged TFM's. The TFM is an older Bob Carver design. The AV-405 is one of a series of amplifiers designed by Jim Croft and his design team, building on their work on the Lightstar II. (This was all after Bob Carver left Carver Corporation.) In his review of the Lightstar II for TAS, Robert E. Greene (REG) called it a "perfect" amp. Jim Croft says the A series, at lower price points, incorporated some improvements over the Lightstar II! The A series amps differ only in their power output, according to Jim. These amps were designed to have flat frequency response into any speaker load, to have the shortest possibe signal paths, deliver high current, and produce low distortion.
I have two AV-705x Premiere's that I use in 2 channel mode in different systems. They are, as far as I can tell, characterless when compared to any other amps that I have ever heard, and I almost always hear some character in an amp. Very powerful, very quiet. REG has one of the A series, as does Paul Seydor who also writes for TAS. Audiogon member "danvetc" is very happy with his A-760. We are pretty much in agreement that Jim C solved the amplifier problem.
People who say that there is anything wrong with the A series amps either haven't heard them or are hearing things that are wrong with the rest of their systems or simply prefer some sort of coloration from their sound systems.
So, don't sell the AV-405, unless you replace it with an AV-705. Even if you insist on getting the Krell, keep the AV-405 and come back here and tell us about the comparison.