Yup, IMAX's "MPX" is little more than a largeish movie screen, with typical sizes around 18m by 8.5m (58' by 28'). MPX maxes out under the size of a "classical IMAX" display, and as far as I can see it exists just about solely so multiplexes can tack on additional IMAX surchages on your ticket.

That "innovation" is >5 years old: http://www.bigscreen.com/journal.php?id=1505