Whoot? My comment is removed, or did I forget to sent it?
Well, I have nothing against safety, but it is useless, if an amplifier outputs lethal Voltage. And call 90V not lethal. It is not as dangerous as 325V i.e., but still dangerous and unsafe to touch.
If ATX Supplies would be very cheap, I would put them in series, with disconnecting the earth from all, but one. This would work with no problems at all, but is not cheaper at all, it might be the most expensive version.
Well, at least you get a regulated voltage. ^^
But is it save, to pull so much power out, without using fans? If you use fans for all, you would have such a loud sound, that the amp is useless. I used a very old ATX supply for my small Subwoofer, but it is just pulling out about 15Watts max, so there will not be a dangerous temperature rise. Pulling out all the power or at least 50W per supply could be dangerous without proper "heat extraction".
So, a toroid is not cheap, but the cheapest solution for my problem. Also: You will be happy about the "safety", because it is mains insulated. Why do SMPS for that high power and "high" voltage outputs cost so much? way over 200€ is not cheap or even close to that.