From Four 12 inch Woofers To Eight 12 inch Woofers, Will I Get Deeper Bass Or More Bass?

If you follow the methods for integrating a subwoofer suggested by "The Sound Doctor," you should have no problem with a sub in your system. Here's the link ... http://www.soundoctor.com/whitepapers/subs.htm

Well, then, mitch4t
it appears that you are all set...

In a real sense, more bass and deeper bass are the same thing.

Bass rolls off for any given distortion spec and any given roll-off (deviation) at a given frequency. So...

If you want bass at -3db to a 90db reference level at X% THD, your current setup will roll off at (purely illustrative example) 35hz.

Because you have added more surface area to your woofer array, the woofer excursions will now be shorter at 35hz. Because THD increases with excursion, you have effectively cleaned up your bass at -3db at 35hz. It’s now less than X%.

You’ll now find that, for the same X% THD at -3db from your reference, you can crank the system an extra 3db. X% THD Bass will now be available at (say) 30hz -3db. You may have to adjust your main speakers at the x-over point to maintain flat response, but you will get “deeper bass” from the new set up, all else being held constant.

68pete, according to all the posts I’ve read here on the ’Gon regarding integrating subs into full range speakers seamlessly, it sounds damn near impossible. 

This is for 2-channel listening only...this is not a home theater application.

Go with subs for deeper base

jafant...I'm very familiar with the Kappa 9 and the power that they require.  That won't be a problem.  I still have the Pass amps.

The whole reason for this approach is to get more bass in the room to emulate the Infinity IRS Beta speakers that I have.  The Betas are excellent speakers....when they are good, but can be inconsistent in the bass area on some recordings and are showing their age (31 years).  The Kappa 9 are extremely consistent on all recordings.  But, the Kappas are no match for the Betas in total bass output and depth (16 hz).  I've entertained adding a pair of subwoofers, but I cannot get a consensus on whether or not a subwoofer will seamlessly integrate.  I do know that adding more of the identical woofers and amplifiers will give seamless integration.  The max I'd like to spend on a pair of subwoofers is $4k period....but, anything but perfect integration is out of the question...I just won't live with that.

Very sweet speakers - mitch4t
You will achieve more Bass by adding the additional (4) woofers. Are you still using Pass Labs power amps? These speakers crave high power and higher current reserves to reach their peak performance.
Happy Listening!

Just more bass! Not any lower! Eight 12's? Sell those hard-to-drive Kappas and get a pair of nicely restored Bozak Concert Grands - each has four 12's - total of 8 per pair! Rudy Bozak made some of the best speakers of the 50's and 60's! A man ahead of his time!