In case anyone was wondering why after the OP replaced the fuse that it died again shortly after but the fuse was ok.
Fuses are in place to protect from instantaneous overload or an electrical fire. If your receiver's fuse blows during normal operation assume that a part other than the fuse has gone bad, replacing the fuse will increase problems. If the receiver blows a fuse because you just had it up too darn loud and a transient sent it over the edge then it might be worth while to replace the fuse and try again without being crazy with the volume knob.
In most cases when a fuse blows it's the former, a part has simply gone bad. That bad part can create more problems for the receiver or worse start an electric fire if the circuit remains closed. By replacing the fuse you close the circuit again.
Digital amps don't have a change in operating voltage or thermal load like an analog amp does, they in most cases have the same voltage input to the digital drive stage at all output levels (Sony actually does vary this voltage I think as part of the volume level), but no possible normal output should cause any problems. A short or using speakers with too low of impedance will cause problems, but not the volume setting unless it fries a speaker which shorts out in death.
From the poster looking for a digital C board, that suggests that it is not a problem in the output stage but perhaps in some sort of intermediate or monitoring stage. What would be good is to have someone knowledgeable look over one of the failed boards.
As for replacing fuses, some risk does exist, but as long as the exactly correct value fuse is replaced I don't see a great risk in replacing it once or even a few times during testing. Each time it is replaced with the fault still present and blowing the fuse does increase risk of damage to other parts, so don't replace it after the first time unless you have actually fixed something.
