Death Knights of Krynn had music. FRUA's 'Evil March' was Lord Soth's theme, and FRUA's 'Mystery' was the Dargaard Keep theme. FRUA's 'Foes' and 'Battle' were the Dark Queen of Krynn battle musics (which I think were overused).
Sadly, the Pools of Darkness themes didn't make it into FRUA, which I thought was a shame.
BTW, I've confirmed that you can remove a character from Curse and stick him into Gateway. It's fun running through the game with 10 Fireballs.
I see two possible 'grand campaigns' here:
Pool-->Curse-->Gateway-->Treasures-->Pools. Lets you keep your stuff from the end of Curse and avoid playing Secret of the Silver Blades, but you miss out on the +5 stuff from Secret, and assuming you're two levels up from 11 at the end of Treasures (given the rules on XP overflow), you're still only level with fresh characters at the beginning of Pools.
Pool-->Curse-->Gateway-->Curse-->Secret-->Pools (don't play) -->Treasures--> Pools. You lose your stuff from Curse, but as people have suggested, you could use Treasures to buff up characters dualled at the end of Secret, then bring those guys to Pools.
I suppose you could finish Pools and then play Treasures, but that seems to have value only as a speedrun. 35th level? Only to see if you can take down Freezefire with a single Delayed Blast Fireball.
Edit: bringing any of the 'special name' items such as the Sword of Stonecutting or the Sword of STalking into Pools does produce weird names (long strings of underscores, strings from elsewhere in the game like 'MUNE TO ELECTRICITY'), although--at least at first glance--simple weapons do seem to behave normally despite their names. The Farrberjik Lined Boots now cast Mirror Image, and the Potion of Spell Enhancement doesn't seem to do anything, though if it increases your casted spell level by 1 I guess it's hard to tell.
You could have fun bringing all the weird items in and seeing what they do, I guess.