Will this amp trick work for increasing bass performance?

Robert,

I believe you are on the right track. You probably don't need a sub unless you are listening to EDM or at concert level volume. Focal recommends an amp up to 500 watts, so depending on how much bass you are looking for I would get an amp as close to 500 watts as I could afford. You have a large room which makes it easier to over drive an amp powering the low end if you going for high volume.

Adding eq can help tailor the sound even more if desired. If you are looking for that chest thump you could further accent the 40 to 80 hz region with out boosting the 160 to 220 hz area which can start to give you that hollow, in a tunnel type sound, depending how surgical your eq is.

I believe that Pass amps and pre amps are truly balanced so if you convert the balanced output to RCA I believe you will loose 6db of out put

Thanks @audiorusty, will keep that in mind. 
Just auditioned a McIntosh pre amp with built-in EQ. That solves my problem in one go.
Someone said an EQ downgrades the quality of the music. “So does a room”, was the sales advisors reply. “It’s a very small trade off, but think of the EQ as a room correction tool”. My system will be in the living room, so I’m very limited in terms of room treatment. 
Also looking at Wilson Audio Sasha and Alexia Series 2 now. They only spec the minimum power, not maximum.
The Alexia’s had muddy, boomy bass despite the room being properly set up. The sales rep assured me it’s because the 350 sq ft room is too small. And this won’t happen in my 860 sq ft living room, with large openings to the kitchen and study. 

Get separate amps for the Bass section ,one for each speaker of course. Class D is the best for Bass.
Something like the Crown that were mentioned or Parasound .You do not need hi-end amps for the Bass section. Save money by using an amp that has high power out and does killer Bass.

Robert1976 wrote: " Anybody an idea what @millercarbon meant by a “$3k DBA”. Any links to a product like this?"

Millercarbon may have been referring to a subwoofer system I make which uses four small subs and costs a little over three grand. Briefly the premise is that room interaction issues are the biggest problem in the bass region, so the idea is to spread multiple bass sources asymmetrically around the room, each interacting with the room differently, the sum being considerably smoother than any one alone. This concept can be (and often is) implemented quite well using subwoofers other than mine.

However you made it clear that subwoofer are not desirable, so I would guess that four subwoofers are even less desirable!!

Imo your idea of using two amps and making the amp driving the bass section a bit louder than the other amp can definitely make the bass a bit louder, but it’s arguably "painting with a broad brush". It looks like the crossover is at about 220 Hz, which means that the bottom 3 octaves or so could be boosted. Imo you run the risk of any room-induced response peaks being exaggerated if you boost everything down there, and those peaks will make the low end sound fat and sluggish.

In my opinion it might make more sense to use equalization which will allow you to tailor what you’re doing in the bass region with a fair amount of precision, assuming your speakers already have adequate extension. (If your speakers do not have adequate extension, and you have a big room which implies that a lot of power is needed, imo EQ is not the way to get adequate extension - you’d be better off with speakers which already have it.) If you’d rather not have an equalizer in your signal path north of 220 Hz, perhaps you can find an analog equalizer (which would have no latency) that could be inserted in the signal path of the lower-frequency amp, south of 220 Hz only. And I agree with those who suggest you not overspend for that south-of-220 Hz amp.

Duke

edit: I had overlooked your post where you mention your dealer’s comments and suggestions. What he said makes sense to me. I think you’re in good hands.

One other very important point...finding the best bass is also extremely dependent on the location off the bass driver in the room as well as the phase adjustment of the bass speakers. The room has bass cancellations and that you can't eliminate. However these cancellations are movable especially at the listening area and it must be corrected for optimum sound.

Once again the advantage to a movable pair of subwoofers is the only way to go if you're looking for exceptional sound. Once positioned in the best 'location' for your particular room, then they are individually 'tuned' by way of phase adjustment to help eliminate (minimize) any cancellation occurring at the sweet spot.

There will always be wave cancellation in a room. It needs to be dealt with. Stationary speakers in a set location unfortunately give the least amount of options for correction of these dead zones. You can NOT power or EQ your way out of wave cancellation.

The best sound is not achieved by placing the speakers in the most visually appealing room location. It just doesn't work that way. Physics rules.