Magnepan 3.7i vocals sound harsh

The higher ohm fuses will only attenuate the high frequencies and will not affect midrange where most vocals live. Try diffusion but I doubt that’ll address your issue. I tend to agree with an earlier posting pointing to this harshness as a possible sign that the amp is straining although the harshness should normally be more evident in higher frequencies.

I did it spent above my means and bought a Pass 250.8 and XP 10 pre.
While the Parasound Hint was a great match with the 1.7i the sound wasn't the same with the 3.7i. The Pass takes control and is more musical in every aspect as it should be at 5X the cost.   There is still some grain in some 60's rock but I'm guessing this is just bad recording.

Congrats on your Pass X250.8. I’ve not heard the XP 10 pre but I’m sure it’s very good. I use an older X250 and love it with my ModWright LS 36.5. If you’re not using good balanced cables I would recommend that and don’t use the stock power cords regardless what the Pass manuals state; my X250 manual stated aftermark power cords don’t make a difference but they do. Hopefully your X250.8 and other components have dedicated circuits or you’re not hearing their best; made a huge improvement with my X250. If you can’t run a dedicated circuit then at least pick up some decent receptacles if you’re only using $2 spec grade which is what most homes have.

Hate to throw in this tidbit after your awesome x250.8 purchase, but a very simple, and easy error for anyone to make, that could cause your issue, is if you have directional cables and just 1 of them is going in the wrong direction.  The parasound is a good piece of equipment, but very detailed and tinnie compared  to the x250, which is amazingly smooth compared to most any SS.  I bring this up, because you mention still hearing grain on 60s recordings....sooo, it is possible that your ear is aclimatized to the reveal of the parasound, and you only think the problem is fixed with the pass labs because of how smooth that amp is...hearing is often just relative perception....take a peak at the directional arrows of all your interconnects and speaker cables.  If you find 1 that is turned wrong, be prepared for your audio nirvana.  If that is not a problem, then hopefully at the very least this comment might help someone else in the future that does make that exact mistake.

I currently owned a pair of 3.7i driven by the CAD 120S MKII, eight high power Golden Lion Genalex tubes, four NOS 6SN7 tubes fed in from a CAD preamp tube with four NOS Telefunken tubes for LP, and two NOS 6SN7 and two high power 6SN7 for CD. They sound rich, warm, lush and full at mid range where all male or female vocals are near life like voices.