I hate to bump a thread that's too old. However, I have in my listening area what is essentially an earlier incarnation of this amplifier, but in the form of a receiver from Yamaha. The model is the RX-496, which was on the market in 2001 / 2001. It still has the motorized POT for the volume adjustment, the continuous variable Loudness control, etc. like the A-S500 amplifier has with one exception, my RX-496 does not have a subwoofer pre-out like the A-S500 amp does.
I'm finding "B" stock versions of this amp for $289 (US $$) on eBay and will probably pull the trigger within a few hours to purchase it. I've used my Grado woodies with the Magnum drivers connected to the RX-496 with my custom extension cable. I used the variable loudness control and I thought the sound was very good. It sufficiently provided good quality audio output to my headphones. Normally, I won't listen to headphones in that area much, if at all. It's more for my speaker listening area where I'm running a pair of Monitor Audio RS-6 Speakers and an Elemental Designs subwoofer along with a Squeezebox to serve up my music. I connected the subwoofer to the "B" speaker channel by using a car audio speaker --> to "Line out" connector so RCA female jacks are now present to hook my sub up.
My RX-496 is very capable and just exactly what I was looking for. I've tried for many years by going through a dozen or so home theater receivers that I thought would provide sufficient 2-channel with a sub listening. I've been quite wrong, my journey has been long and a bit expensive if you consider that I probably lost $100 on each receiver transaction.
So, with my RX-496 performing so good, one might ask why I'd opt for the A-S500? Well, due to the cash I have in PayPal from dumping off my home theater gear, I have the capability to buy the amp and try it out. In the review from What Hi-Fi, they specifically noted that the amp would pair well with the speaker offerings of Monitor Audio, so I feel as though I'm good to go in that area.
If I do pull the "buy" plug, I'll come back and post some impressions in a few weeks because it will take me about a week to receive it.