Sony XA5400ES fuse directionality...

Oh Boy!
Rrog

Dang Rrog, you beat me to it. Although my thought was, oh brother.
So now I'll make a suggestion. Try the fuse one way for a week, listening critically of course for the differences/improvements the fuse makes. Then switch the fuse around and repeat the procedure.
Once you've got the results you can start another thread explaining the results. I'm on pins and needles.

It looks like the fuse in on an AC line which means no matter how you install it it will be in the right direction 50% of the time.

There are two fuses in the unit, and I was hoping to find someone who was familiar with it before I had to test the directionality by ear, which I have done before with my amp and it's single fuse. It seems to take a about 100 hours for the fuse to "break in". The latest Hi-Fi Tuning fuses DO make a sonic improvement to my ears, and I feel they are worth the $50 price tag. I know that there are some doubters out there when it comes to fuses, AC cables, speaker wires etc... but I am not one of them. They certainly won't make you think a drastic improvment has just occured by upgrading to one, but these little 5% improvements all add up and contribute to the overall sonic "picture".

They can make a difference around 4k hz. Some people like that.

They make no difference. Try to return them if you can.