I have the 5000R, and have listened to the 4000R a lot too ...
it depends on the price you can get them for ... I got the 5000R for 784USD (yes expensive over here) and I still feel its very worth it.
first off, you get a remote ...
then you get the loudest subwoofer for its bracket range (5000R; SPL wise)
you get a class d amp (5000R)
and I feel that it is very very sufficient for both HT and music, it gets me 90% satisfaction for a lot less money than my other sub.
I honestly could have gotten away with being satisfied with this one rather than getting incremental improvements for 50% more and then 300% more money.
but buckeye and the other guys are right ... if you're a regular audioholic who has upgradeitis, this one doesnt plumb as low as other "cheaper" subs. the subwoofer driver doesnt have much excursion (not that it needs it) ... and of course compared to the internet direct companies, doesnt stand a chance.