Spell Matrices and Multi-Disciplines

[Reyntrannin]

Thank you for all the input. i completely missed where my question was answered in the rules, so I feel a bit silly. however, the earlier conversation etherial linked really helped with the brewing argument.
It's also good to hear that the multi-caster concept shouldn't require much tweaking on my part as GM to keep it in check. Now it's down to determining if the combination makes sense role-play wise. My player's got a good argument for up to three, but the fourth one is always at best a stretch, so I'm thinking I'll have to limit it to three and he can either give up on the last one or play human and do it via Versatility.