Hi Dave, as you know the damned Accuphase boxes are expensive and addictive (once you have one you will want more). So in the last 4 years or so I've listened rather extensively to quite a few Accuphase units. I did my homework well before both Accuphase purchases.
Of course, these are my opinions so what I have written in my previous post was in no way meant to upset you. Also, my experience with the current models (e.g. E-560 and A-46) is not that extensive. However, IMO the main difference between these models and their predecessors is mostly in the drive, i.e. they sound louder for a given watt indication on the Accuphase meters.
Here are my answers to your inquiries:
The E-560 as a preamp is inferior.
Firstly, about 1.5 years I wanted to buy a A-45 power amp and used my E-550 as a pre-amp. My dealer advice me against it. Then, I wanted to buy a C-2810 and use my E-550 as power amp, and again the dealer advised me against this move. The guy had no agenda as he was the one selling both units. Secondly, somebody I know used for a few months an Accuphase power amp (P-650?) with an integrated Accuphase integrated (E-408?) as pre-amp. The integrated sounded better by itself, however, the integrated was easily outclass after my friend has added a C-2400 pre-amp.
Of course, these are just stories and I did not tested the E-560 as a pre-amp in combination with an A-46. However, as I have mentioned before you loose a lot of flexibility with the E-560 as preamp, e.g. no balance outputs, no selectable preamp gain. Both can make a significant difference (especially if louder listen levels are needed). Also, the C-2110, C-2410/C-2420, etc. are fully balanced design (separate power supplies and AAVA modules for left and right channels, etc. ). Why would Accuphase go through all this trouble if they could print the whole preamp circuitry on a single board (like in the integrated amps)?
The A-46 will not go much louder, when the Accuphase representative told me it would.
Firstly, as Bgpowell has pointed out, 15 watts will not make such a dramatic difference. Secondly, that was my experience with the E-550 vs. the A-45. Now, as I've mentioned before, A-46 will play much more relaxed than E-560 as it has much larger power reserves. That means that the sound will fall apart much sooner with the E-560 than with the A-46. So you can say that the A-46 will go much louder. This brings me to your the last point.
The P-6100 is a better choice than the class A power amps when listening to large orchestras and big bands.
Sound-wise the differences between the Accuphase class A and A/B are not that significant. If one listens to loud volumes and/or music with large dynamic variation (e.g. big bands and large orchestras) then it is better to choose the class A/B power amps, as they are much more powerful and will not clip as quick as the class A ones. One can not be happy with his units if he sees that it is constantly clipping - even if one does not hear any sound degradation durring clipping. Also, it is not a good idea to constantly drive the amp beyond its capabilities. (I have seen the A-45 clipping, while the E-450 was louder and nowhere near clipping; of course, the E-450 was never as refined as A-45). Finally, note also that the large class A/B amps will also have a better grip on large woofers then the class A ones.
I hope that this clarifies things a bit.