Voadam
Legend
Races mix fine.
Nonmagical classes mix fine although warmains slightly out-tank fighters.
Magical classes mix OK but add in another magic system so you have arcane, divine, psionics, and AU.
AU spell classes are more flexible but generally have a little weaker spells in direct punch.
D&D spellcasting classes are based more on exponential power increase while AU classes are designed to be a bit smoother in progression so they are more powerful at lower levels and less powerful at higher levels.
The spell template feats are usually based on gp costs so the level of campaign wealth can affect their power balance.
You have to decide between a few minor rules differences (tumble static DC? sneak or move silent and hide?).
Mixing should work fine as much as you want to incorporate.
Nonmagical classes mix fine although warmains slightly out-tank fighters.
Magical classes mix OK but add in another magic system so you have arcane, divine, psionics, and AU.
AU spell classes are more flexible but generally have a little weaker spells in direct punch.
D&D spellcasting classes are based more on exponential power increase while AU classes are designed to be a bit smoother in progression so they are more powerful at lower levels and less powerful at higher levels.
The spell template feats are usually based on gp costs so the level of campaign wealth can affect their power balance.
You have to decide between a few minor rules differences (tumble static DC? sneak or move silent and hide?).
Mixing should work fine as much as you want to incorporate.