The only difference of M802 and 801 at your place is...........you need to spend more to upgrade your amp section. I dont think B&K has good enough power to drive M801 well.
When I was working in a shop that sold both models, I actually preferred the balance of the 802. The 801 will better it, though, for sheer bass weight and slam (but will require a brawnier amp). All in all, taking the size, weight, appearance, and price into consideration, I would have taken the 802's (especially for average-size rooms) even if they sounded the same except for the bass. However, I found the 802 to be generally smoother and more listenable. Given that the mid/tweeter modules are the same between the two models, I would have to assume the difference lies either in the way the 801's 15" woofer must be crossed-over to the mid, and/or the demands it places on the partnering amplifier - either way, what the big woofer can gain you in the low bass seems to be prone to extracting a similar price through the mids. But I should add that my exposure to various set-ups with both speakers is somewhat limited (amplification on both tended to be big Levinson and ARC SS, cables Transparent or Monster, speakers were set up in the same large room), so my impressions must likewise be qualified.
802s are easier to drive,can go with less power,801s especially the eariler matrix and 2 need a minimun of 200 wpc,they sound great but the 15"woofer needs and eats up power,the dual woofers in the 802 are more tighter in my opinion,and the stands make a difference.I would go with the 802s and it,s not because I own a pair it,s that I was able to hear both the 801s and 802 side by side with S/S and even tubes and the 802s sound better.Cant you see why that the new 802 Natilus when they are up for sale on Audiogon sell very fast.
The Matrix 801 Has a 12 " woofer not a 15, that is in the Nautalus version. I love the M802 and they are on stands. I wonder if there is an upgrade. Would be nice to outfit the Matrix 802 with Nautilus woofers. The dust caps on the Matrix are so cheap looking( soft plastic) The N802 look so much more substatial. Anyone have anything to say about after market crossovers like the Maughan box or the B&W crossovers to lower the bottom end?