MC12HDBEQ owner here who has been using a 7.1 setup with some model of Lexicon processor for the past 20 or so yrs.
What are you missing re: discrete vs L7? Not much. There just isn't that much discrete 7.1 material out there. PL2X or Logic7 both do wonders. Do you watch old movies with mono soundtracks or listen to old mono music? Turner Classic Movies (TCM) cable channel sounds so much better with the Lexicon (only) mono logic modes than any other surrond mode I have ever heard.
I tried the AV8801 in my system for a week and was impressed with most of what it does. IF i had to choose a new processor today it probably would be my choice but i am not so much a fan of the all or nothing /take it or leave it Audyssey. Too heavy handed for my tastes and paying upwards of $700 for the Pro kit and license which is locked to just that specific prepro device doesn't appeal to me.
I would strongly suggest searching out a dealer or local enthusiast and discovering for yourself if it is the right fit for you. New isn't always better and if it ain't broke don't fix itt, right? Then again the grass does seem to look greener on the other side of the fence very often. Prolly just the sun playing tricks .One last thing. The 8801 also has a very good sounding HD tuner section.