There should not be any hum from the amp. Try swapping the tubes between the sides and/or cleaning the tube pins with contact cleaner. It's normal for it to get hot.
I'm not sure what you are talking about when you refer to a "amazing increase in SQ" that many here have supposedly claimed. What were you using before your Little-Dot?
If you're using the same source as you were before and you're previous setup didn't have any major deficiencies, then you should expect it to sound mostly the same. The Little-Dot I+ is good because it's a fairly simple Class-A design, but the effect the tubes have can be much more subtle than you might expect, although it certainly does effect the sound.
I'd agree that the stock tubes aren't particularly great, neither is the stock Op-amp. Changing one or both of these things can produce subtle changes that you might prefer.
To a large degree, it's not about what's best in general, but what matches up best with your headphones. I prefer certain tubes with certain headphones and I have certain headphones that work best on different amps too.
Are you using the stock tubes?
If so i can recommend getting some cheap voskhods from ebay, they are in the EF95 family so you will need to remove some jumpers in the amp but they sound 10X better than all the other tube families when paired with Alessandro MS2is. In my humble opinion of course.
My amp gets pretty toasty too, i wouldn't worry about it
Stock tubes are 6JI, which is interchangeable with EF95, 6AK5, etc and doesn't require a jumper change.
