What's the Sonic Character of Accuphase Amps?

Bryan I can report on the P450 with good authority as I recently bought one to go with its mate (the C275) which I also bought early this spring.
I had been searching for the past 4 years, looking for a combo to better my beloved Luxman Ultimate components when the amp failed unrepairably in '97. I'd tried a number of other lines: Krell, Classe, Conrad Johnson, Ayre, McCormack, Marsh, Perreaux, Sonic Frontiers, Golden Tube; some were more or less satisfying than others, but all left something lacking musically despite the minimalist design approach. I even considered Luxman again but their "product support" scared me away. Looking toward other full-featured products I then discovered the Accuphase line, & bought the preamp sound-unheard. Wow: now I was finally getting somewhere! Resolution & musicality all in one package with every feature that I could ever hope to use. Hopelessly addicted now, I had to have the C275's mate & again bought sound unheard. Wham; this is THE one! Talk about involving!
You've just got to get ahold of one of these amps. Resolution & warm musicality are offered within a very neutral sounding envelope, as Kelly also attests, and it's still affordable. If you have deep enough pockets then I would definitely consider an audition of the A50, which Kelly really likes with his Avalon's & a Tara The One AC cord. My own lineup includes much of Synergistic's better cabling with the active shielding center, and MIT's better speaker cables driving a pair of vintage Belle Klipsch. This 200 watts per channel driving horns is so incredibly dynamic (incredibly crazy too I'm told: hee hee) with an HDCD or an analog front end either way it's just amazing. Another charactaristic of the sound is "completely in control" so much moreso than anything else I've tried. WAY recommended!

Bryan my method for figuring out desired headroom is simply 20dB (times 100) over your average listening power level. I have run that way for nearly 30 years now with very acceptable performance (and only 1 blown tweeter when we once got really carried away). My 100 watt rated horns become quite loud at only 2 watts/channel drive level, so for a rated 200w/ch amp I then have at least 20dB of headroom available (most high quality amps are conservatively rated & do produce around 10% over rated power before clipping). Of course this large amount of power is only used when really pushing it hard, but it does happen (albeit rarely) so I want that capability available. However when I have run with a high quality lower power 100w/ch amp (an Ayre V3 class A design) I found that to be inadequate even with these 104dB sensitivity speakers. The P450 will definitely satisfy your requirement for controlled finesse with dynamic capability, and will do so efficiently (idle power consumption is just 125 watts - not too bad at all). Considering that your speakers also like lots of power, I don't think you can go wrong with that combo.
The thing about pure class A amps like the A50 is that, as Kelly advises, they do have a lot more drive available than their rating would suggest; the peak current capability of these designs definitely belies their lower power rating. Although I've never heard the A50 amps, their price point is simply more than I'm wanting to spend for an amp so it's doubtful that I'd ever actually audition one in my rig. Although I rather doubt that the A50 has near the headroom capability of the P450, its sonic qualities may more than make up for that descrepancy, being a class A design. So don't fuss over the theories & the numbers, just TRY one. As I said previously, if your pockets are deep enough for the A50 (or for two - they are bridgable) then certainly do audition one. If the P450 is more in line with your budget then go with that or one of the other less pricey Accuphase amps.
Another factor to keep in mind is waste energy; class A amps burn a lot of power & produce a lot of waste heat in your room even when sitting idle. In your temperate San Francisco climate, extra heat in your house is fine in the cooler months, but is ceratinly unwanted when it's warm outside as it can significantly increase your cooling bills. If I have a class A solid state amp in my rig during hotter weather then it's often left powered down, & therefor doesn't sound its best even when it is turned on in the evening. Normally I will then change it out for an A/AB design such as the P450, but even that won't be left on continuously if it's much over 80 degrees outdoors. The waste heat factor is another one of the tradeoffs that you'll have to juggle when making your amp decisions. Oh and yes, you do correctly surmise that I'm certainly quite happy with the product line. The manufacturer product support is impressive enough that I'm not worried about a failure in 5 or more years turning the equipment into some very expensive boat anchors. This has always been a problem with my Luxman setup; much as I loved it, I absolutely wouldn't make that mistake again.