Ok, just for completeness I thought I'd post what I went with.

I decided to try the latest DD-WRT firmware (which seems to be based upon a fork of the sveasoft stuff but I could be mistaken). It pretty much does everything I want it to do (DNS masq, QoS, etc). The port forwarding interface is clunkier than I'm used to, and at one point I had to manually clear out some forwarding instructions out of the nvram when the interface got out of sync with it, but it does seem to be working via uPnP and manually.

It also includes the xlink kai daemon (a free implementation of Xbox live) and I'll be testing it out soon. I haven't fiddled with the QoS much yet, but I'll be spending some time this weekend tweaking it with my SunRocket VOIP gizmo (yeah, they really call it a "gizmo") to see how well it works. Knowing the twiddler in me I'll probably wait until I have it working perfectly, then I'll wipe it and rebuild it with something else though

-- Foz