I often buy games together. Recently my two purchases were Astonishing Swordsmen & Sorcerers of Hyperborea and Magical Theorems & Dark Pacts. While not explicitly designed for each other, they share a common DNA in terms of Basic D&D via the d20 SRD.
AS&SH has a number of new classes, in particular magic-using ones. MT&DP is nothing but new classes and spells. AS&SH is a grittier, almost primitive, experience. MT&DP is straight up Basic/Expert/LL with spells that go up to level 10. So where does the commonalty lie?
Ok take the MT&DP classes and limit them to 12 levels only. Typically not an issue. And in some cases also reduce the spells to just 6th level. Use the Magician as the base class. As far as the powers each class gets, well I would deal with them on a class by class basis. Maybe give them some of the spells as powers.
Let's take the classes in detail.
Cleric and Wizard
These classes are pretty much the standard archetypes, use the classes in AS&SH instead and swap out spells as desired.
Elven Swordmage and Elven Warder
These classes can't be used, no elves, but you could make a Swordmage or Warder and split their Casting Ability and Fighting Ability evenly.
Similar to the other Sub-classes"
This class has so much potential in AS&SH. Given the horror elements in the game (and even the mythos elements) this classes takes on a more malevolent tone.
A subclass of the cleric. I would reduce the fighting ability, so "0" for levels 1, 2, 3; "1" for 4, 5, 6 and so on for a maximum of of 4.
Inquisitor, Merchant Prince, Unseen
I think these guys would work a little like the warlocks. The warlock is a bit of a fighter and mage, so these classes are all a bit like thieves and mages.
AS&SH has a necromancer. Just use these spells.
This is closer to the concept of the Warlock
These guys are neat ideas. They are close to what would be a cultist in AS&SH. Spellcasters learning from long lost liturgical texts.
So a lot of really good choices. Honestly there plenty of class choices in AS&SH already, but these can give your game an interesting twist. Plus they feel right together.