Upgrade LSiM 704c to 706c in a system with LSi15?

CaptDistraction

Just changed up my home theater a bit:

Polk LSi15 fronts and surrounds, LSiM704c center (replacing LSiC that I didn't love)

4 in ceiling polk 70rts, some GSG 18" martycubes to cover the low end

new Marantz Cinema 50 receiver, new emotiva XPA-5 amp to drive all the LSi/LSiM speakers

I am thrilled in how it sounds, scored the rear excellent-shape LSi15's off a FB marketplace ad for $200 last week. That said, I can also get a LSiM706C - which I have the room for, but curious if people think it would be a quantifiable improvement over the 704C.

The 704C cabinet is pretty small, and audyssey detection result brings back a pretty flat response and suggests a crossover down to 40hz which is a bit aggressive (though A1Evo also agrees with it despite a rolling filter). The 5.25" bass drivers in it match the drivers in the LSi15 towers (which have their own 8")

The LsiM706C is massive in comparison, a much nicer enclosure and 6.5" drivers. According to Polk's spec sheet, it goes down another 20hz over the 704C and I've seen a number of reviews where people moved from 704c to 706c and liked it.

I'll admit I've got the upgraditis with most of my hobbies, but if nabbing one of these is a good call, I can certainly afford the upgrade, but was curious if it actually would net any improvement (the LSiC to LSiM704C improvement was great for dialog clarity). Room treatment is otherwise where I'm spending a lot of time going forward.

PSOVLSK

I’ve owned the LSiC and the 706, but have never heard the 704. I suspect the 706 would be an improvement over the 704, but probably not as much of an improvement as the 704 was over the LSiC.

Emlyn

I had the 706 but found its cabinet to be too big to be practical. The 704 sounded pretty much the same to me and in a much easier to accommodate size. I kept the 704 I had for many years but got rid of the 706 not too long after I got one.

skrol

I am rather curious about switching from LSiC to LSiM704C. The LSiC is voiced to match the timbre of the LSi series and teh LSiM704C to the LSiM series. Is the timbre close enough?