*You can get a technician to check the bias for you. Its not difficult to do but if you're not careful, a slip of a test probe can cause expensive damage. If you need the service manual, send me a PM and I will reply with a copy.
*IMO, the AC supply should not be causing the issues you're experiencing.
*"DC coupled" means having no capacitors in the signal path. A DC coupled preamp or amp will pass/amplify DC. This can be a problem if for example a source component or preamp has high DC offset. The amp will amplify that DC and pass it to your speakers, which can damage them if the DC level is high enough. Many/most modern amps have DC protection circuitry that will open an output relay in the event of severe DC offset. IMO, high DC offset should not be blowing your mosfet fuses. The CA-200 has protection circuitry for that purpose.