With the Marty Cube and quite a few ported/vented designs, a protective high pass filter below tuning is recommended and you need either separate dsp (such as a
miniDSP 2x4HD) or an amp with built in dsp like the Dayton models you listed that have such. Personally I prefer a rack style amp rather than a plate amp, makes the box easier to build and not having the amp in that environment (of the sub itself) for reliability. Popular amps for this are various pro-amps, the Behringer iNuke DSP series being quite popular and the least expensive (which you probably saw with the Marty Cube threads),offerings from Crown and QSC with similar dsp capability cost more than the Behringer.
While a low tuned ported box can take advantage of efficiency above tuning frequency, it drops off rapidly below it and multiple sealed subs can actually do better due shallower roll-off in combination with room reinforcement (but means likely at least four before any advantage). Just depends how low you really want to go and at what spl (i.e. your spl and extension goals) and how many subs you want
. For two subs I'd go ported/vented.
You have a fairly large room at 13 x 35 feet (ceiling height is what, 8 feet?) for an estimated 3640 cuft...is it a sealed room or open to others? Works on total volume available. IIRC the advantage of the UM18 is power handling and lower extension but I'd have to review (this driver is used by
Seaton in the F18). As to music/movies, thought this system was for both? (echoing Verdinut's questions but he may have missed your room size from your OP).