I think the encounter as described is the one with the mage Rayric Gethris, no? The cowled wizard that Edwin sends you to conquer.
Nice job on defeating him, as early in the game he can be quite tedious until you find the right tactics.
A very simple method involves one oil of speed for your best fighter to initiate dialogue, then to flee back down the stairs to wait for the contingency defense spells to wear off. Its a tad silly, but hey it works. [img]graemlins/hehe.gif[/img] It takes some time for them to wear off, but when they do, he'll only have a protection from normal missiles spell on and so will be easy meat for your fighters.
I don't think tactics from the previous games are that disimilar to be honest, despite the heavier usage of magic and counter spell upon counter spell in SoA. I've come fresh from the first game into this and many similar tactics that I used in it are working just as well in SoA. Its just all relative to the power of your party and exploring all available options to find the most effective tactics.
Thus, Know thy enemy is a handy maxim.