I had purchased a Dynaco 410 a couple years ago and used it with Bose 901 series III's. I recently purchased another 410 and was going to mod them for mono-block operation (600 watts each block) and ended up with a pair of sweet Kilpsch Cornwalls. The 901s now sit dormant and I bought a Dynaco 400 figuring to replace the pair of 410s. Either amp is overkill for the Cornies, 1/4 volume will shake the paint off the walls.....in the neighbors house! My opinion: During dinner I listened to Santana for a while with the 410. After dinner I hooked up the 400in place of the 410. I listened to Santana "Samba Pa Ti" a few times and my reaction was a "harsher" midrange particularly in the guitar solos (well its almost all solo, LOL), on the 400. Want to try it earlier in the day so I dont bug the kids. A minor bug was that I am not really sure what levels the amp attenuators (line in volume controls) are at. I keep wondering "Are they at symmetrical levels?" Without a sine generator and and meter or scope my ears play tricks on me trying to decide if one channel is louder than the other. I can easily make a test tone CD and calibrate by ear, not wanting to drag my O'scope home and perhaps I will do that. Need to listen to each amp a little more, will require swapping out a few times! Anyone else have experience with 400's or 410's"