Would like to get more bass out of my B&W 801 series 2 speakers

My living room is large like yours and seems to just swallow up bass. My prior speakers did not work at all there but were gloriously full in a more moderately sized room. Do you have the ability to test that out a smaller room as an experiment? My fix was a larger more efficient speaker but subs can work wonders too and you can dial them in to the level you need. Also an amp with a different sound profile might do better for you.

@ditusa wrote:
Why not connect your JBL subwoofer up?

The preamp I am using has issues with the sub out, so I would have to apply a filter to speaker output in order to drive a sub.   

Regarding finding a mono signal to test my existing amp in bridged mode, it looks like this is easily accomplished with the minidsp 2x4hd.   I have been thinking about getting one of these as it appears to also be a solution to my preamp/subout problem.    I can use it as a digital filter to convert a regular speaker out to sub out.

Lots of experience with that generation of B&W 801.  My friend still runs a set driven by a pair of bridged GFA555s.  When I hear them I remember why that was a speaker that always sounded right to me, even today. I did have to rebuild both his crossovers last year because the high-pass caps for the midranges fried, but the midrange drivers remained unscathed. Whew!  I hope your crossover mod addressed that issue. B&W did offer around this time an EQ that was placed between the amp and preamp.  If I remember correctly, the EQ changed the woofer roll off from a 4th order to a 6th order Butterworth alignment, adding a half octave more of bass extension and a steeper roll off below that point.  They are still found on eBay occasionally. Krell made one too but they were very expensive and really didn’t sound any better than the more modest B&W option.
In all, I agree with others that a LARGE subwoofer, or two, might be your best solution especially considering the size of your room. Though I do remember selling a pair of B&W 801s and a brace of Adcom GFA565 monoblocks to a couple who wanted to take advantage of the casters on the speakers so they could roll out their speakers onto their outdoor deck to provide proper music for their lakeside parties.

Are you using the stock power cord on your amp?