My studio monitor is sad. Is this a good place for amp diagnostic advice?

[indianajo]

if this is the first repair the OP has tried, I would suggest initially changing as little as possible to return the amp to correct operation, and possibly follow-up with further work if needed and confidence is gained. Changing too much at once and breaking things accidentally would be a tough one to recover from. The original caps have come this far (most of them…) so no reason not to let them work a little longer, having gained knowledge on what to look at if further problems arise.

I agree with changing 1 or 2 parts at a time followed by a test to make sure one didn't just inject an additional problem with bad soldering or the wrong part or placement. Sound or performance got worse, back up one step and look carefully for a mistake.
However, buying 2 parts at a time involves a $9 freight charge repeatedly, plus maybe many handling charges for too small an order. Buy them all at once, replace one at a time. Plus if you wait for caps to fail one a time, the product is broken all the time and you have to take the case off over & over.
I've repaired an Allen organ SMPS with shorted mains cap that blew a thermistor, plus scrapped serveral flat screen TV's (for the INXS FET transistors & heat sinks) with exploded mains caps. One SMPS in a Peavey amp had a power supply 5 v supply cap blow a thermistor. Why would a M-audio power amp be any more resilient? Plus the observation in post #17, "cap top" is not one of the 5 usually reliable ecap suppliers, Panasonic Rubicon Nichicon Vishay Kemet.

 

[valgamaa]

I guess you didn’t read my earlier post, where I suggested buying replacement caps for both speakers for the very reason you highlighted. As a first repair, however, I stand by my original comment “initially changing as little as possible to return the amp to correct operation”. The other caps will fail, but get the speaker working properly before moving on to preventative maintenance.