How many fuses in a McIntosh MC275?

you can only prove hearing improvements on the blind a/b tests. blind tests is where all audi'o'philes fail to ID stock fuse from aftermarket and other silly unnecessary stuff.
as you know, fuses tend to blow and usually are all visible on the pcb or direct wiring. the improvement you've heard is possibly from the quality of the contact so all you need to do is to clean fuse terminals with qtip and contact cleaner.

I read the schematic and found that the two fuses inside are actually for filament heaters, not speaker outputs.

Nothing wrong with blind tests per se but it's certainly a mistake to think that if someone cannot hear a fuse or whatever in a blind test that the fuse or whatever doesn't work in other systems. There are many reasons why audiophiles get null or inconclusive results with some tweaks. You know what I'm talkin' about.

Marakenetz, do tell of your experiments with blind tests of standard and audiophile fuses. Of course it would be disingenuous to suggest someone's direct experience was to be false or untrue due to an improper scientific method if you had not rigorously proven the null hypothesis yourself (adjusting for clean contacts and such).

Hififan: my mistake; it's a 2 A fuse because my amp runs on 220 V (it was not 200 mA).

Thanks for the link to the service manual. You mean the two fuses called F1 and F2 on page 8, right? So if they are on the filament heating circuit...should I expect them to improve sound?

Thanks for the input!