There is no denying the superior quality (general quality) of the Arcam brand. But the lowest price I found on an Arcam A85 was £350 on Ebay. The correct current prices for the Yamaha are AS300 = £199, and the AS500 = £279.
They Yamaha are new with full warranty and dealer support, but they are not Arcam.
The Arcam very likely is used, and while it might be an exceptional bargain even at the higher price, you have to ask how much you trust the sell to represent the product accurately and to ship it properly?
Both the Yamaha AS500 and the Arcam A85 are rated at 85w/ch.
The Arcam has a lot of features, but most Arcam amps don't have tone controls, I'm not sure about this one. If that matters to you, then take it into consideration.
I would say, that the Arcam is probably on the low end of premium amps, though the DIVA A85 is not the highest in the Arcam line. The Yamaha are probably, just a little above mid-pack in consumer electronics. So, certainly Arcam is better quality. But, at the same time, Yamaha is not a bad amp, and is exceptional value.
You have to weigh New vs Used, and weigh features, then decide where your priorities are.
I found a
Stereophile Magazine review on the Arcam DIVA A85, and the original selling price was US$1499, which would be about £990. Though I couldn't find the actual new selling price in the UK.
Arcam DiVA A85 integrated amplifier | Stereophile.com
So, certainly Arcam has the superior quality, but I suspect it will be difficult to find one for under £300. The A85 was new on the market around 2001 from the research I've done. So, more than 10 years old. That is something to consider.
Just a few thoughts.
Steve/bluewizard