Sorry to be vague . . . I just meant to weigh in on the preamp issue, not the headphone/system matching issue. The MG Head is pretty good as a preamp for the AV8's, and it's comparatively cheap for a tube preamp. But, for dedicated preamp service, you can doubtlessly do better. Still and all, unmodified AV8's are not going to "change your life," regardless of the preamp used. But what do you want for $99 a channel?
Plus, I haven't done it yet, but I'm betting $35/channel worth of mods will turn these babies into a category-owner. 'Bout $50 worth of mods into my MG Head, and it's in a whole new class now.