Replacing fuse

I heartedly agree with almarg's position.  In the big scheme of things, 1.7A difference is not a whole lot when you are looking at a 6.3A reference point.   And it really varies depending on manufacturer.  A 6.3A fuse is relatively equal to 756 watts of energy.  Bumping this up to 960 watts with an 8A fuse is likely not going to make much difference of where the fuse breaks/melts, especially since this is probably going into an amplifier which will use a lot of current anyways.  I would say that using a 10A or more fuse may start to border on the "too much" scale.  The bigger amps that use 10A  or 15A will have a lot more power supply and circuits to spread the energy around before it hits the "too much" threshold.

I have seen some manufacturers that are right on the edge of what the amp will use (watts plus overhead/waste) and others that are 2-4 amps above what the electronic device is scoped for.

Generally speaking, a higher amp fuse is a thicker wire with less resistance.  It will allow more current and faster current through to the device and the result can be improved dynamics and punch/power in the sound.  There is a point where it doesn't make much difference.

john421 likely purchased one of the clearance fuses from Parts Connexion.  These are probably either Hi-Fi Tuning Gold or Hi-Fi Tuning Silverstar, selling for around $15 or so. 

@falconquest - in response to bumped up fuses.  I did say "generally speaking" and also said "there is a point where it doesn't make much difference".  I have heard definitely improvements on bumping up a 1A fuse to a 2A fuse in a preamp.  Heck, I have even heard improvements in going from 1A to 1.6A.  The sound with the larger 2A just hits with more authority, more power and better resolution.  However, that's the most I will go.  I have seen some preamps that use a higher amp fuse (such as a 2.5A in a Krell Phantom), so a 2A is not out of the ordinary.  Usually, these larger amp fuses make more of a difference in preamps that use Class A circuits because they are such current hogs.  Things that use normal op amps or a small amount of op amps may not benefit as much with the larger fuses.

The difference between 6.3A and 8A is going to be a lot less - probably too small to actually hear a difference.  But there could be a -very- minor improvement.

As far as these NASA comments, either they are a troll or coming from an inexperienced point of view.  NASA will have completely different requirements for their fuses - such as extreme reliability, exact breaking/melting point, ability to support high speed digital circuits, etc.  They will not have the same requirements as far as allowing the voltage into an analog equipment to sound pleasant or with a specific character.