507u is quite a big jump from 505u in terms of driving capability, clarity, depth of the stage and the overall smoothness. my local dealer here have all 505u,507u,509u, and 590A II in demo. i was lucky to have a chance to do a/b/c/d/e comparison with all of them along with a gryphon diablo. before i went there i was targeted at 507u simply because i thought it has newer circuit board, only 10w difference with 509u and it's 2.5k cheaper. the speaker was a pair of triangle megallen bookshelf, cdp was a luxman d-08. i first listened to 507u and overall i was quite satified though i found it was a little too ss sounding for me. switched to 590A II, 590AII had a lot more body and weight in the sound nodes, its definitely a thick sounding and musical amp. the 507u did better on high/low extension but could not match the well defined sound nodes and smooth presentation of the 590AII.
and then i switched to 509u, i was confident to say 509u was in complete different class with 507u and 590AII. it had the smoothness and body just like 590AII with just a tad thinner sounding. soundstage was so open with a lot more depth, what i liked the most was the authorities and powerful control of the entire frequency spectrum that you could not find in 507u and 590AII. 509u was able to portrait a complete stage while listening to orchestra. high/low extension was extremely well and stable.
i finally bought 509u even though that was out of my budget but at the same time it did so well that was beyond my expectation and now i couldn't be happier. i compared it with gryphon diable and i would say they were in the same class. gryphon had more powerful bass and sedutive vocal, however, it lacked depth, sound seperation was even worse than 507u and highs/details was not so great at all
