Mac,
A lot of your experience with removing subs could be explained by the x-over frequency you were using prior to losing the subs. If you were crossing at lower than 50-60 cps, I'm not surprised that there's little difference in "slam" w/o the subs. The Maggies were doing (very nearly) all the work in the "slam" region, anyway. Unless your program material was unusual (pipe organ, a handful of solo piano recordings, etc), the subs were doing a different job (adding weight, ambience, and mid-bass "clean-up").
If you were crossing above 70hz, you'd probably hear a more obvious difference in "slam". Even that, however, will depend on program choice. For kicks, try crossing the subs at >100hz with the SMS, then remove them. In this case, you'll hear the effect with a lot of recordings.
Marty