Thanks so much for your help! Can you give me a reference track you use and what to listen for? 'sounds better' is a little vague for this Engineer... : - )
Kerry, I don't think it's so much a particular recording as I suspect most any recording you're familar with should do. Here's one you're obvioulsy familiar with but I don't know if it helps as a direct response to your questions here or in your OP.
In my case, my subs' current crossovers are set at about 82Hz. I've not spent much time on this sector of dialing in my subs but what I listen for first and foremost is to ensure the bass is tight and uniform with the mains. The subs drivers and main speaker drivers voice coil fronts are hopefully within a 1/2-inch of each other from a listening chair perspective so phase does not appear to be an issue. After that, what I've found myself listening for or at least noticing primarily is potentially additional ambient information, warmth, and improved balance in the overall presentation. Others obviously may notice other things but that's what I've noticed most. I've got the x-overs set at 82Hz because the time or two I've set the x-overs between 82Hz and 120Hz, I've not noticed much of a difference so I prefer to save the subs' amplifier juice for the regions that impact most.
I should also note that my VMPS RM-40 speakers are each equipped with two woofers and a passive down-firing radiating woofer and I was never able to or I gave up attempting to dial-in the mains to the nth degree. IOW, in my case, although I thoroughly enjoy the VMPS speakers, their bass is perhaps their greatest weakness in my current config. Hence, once dialed in, the subs seem to provide the necessary augmentation to make up for that weakness. So I'm kinda' liking the 82Hz x-over.
Hope this helps,