I'm going to suggest you take these units in to a proper electronics service center and have them checked out by someone who troubleshoots this sort of stuff on a day-to-day basis. Normally I'd be all for going it DIY but you're dealing with high powered electronics. There is no room for error here. If you screw this up the result could very well be death.
Blue Sky's contact page lists their global resellers. If you're not in the USA you'll probably need to get in touch with the local reseller to figure out who might be authorized, near you, to service them. You could start by emailing email@example.com though.
If you're not concerned about warranties and such on them, just about any audio-oriented repair shop should be able to troubleshoot this kind of thing. The amplifier topology should be common enough. Anyone who deals with home theater amplifier repairs or if you've got pro-audio repairs for sound support should be able to take a look at them for you.