I'd agree that, but I had the same Klipsch 5.1 and when I upgraded ULS MK2 I was blow away by that subwoofer for both movies and music. That little sub packs some deep bass punch that 100% justifies the price tag. I would't overlook this sub. Don't crucify me for say this, but from my personal experience I would say that just because your speakers are ported it does NOT mean you have to have a ported sub. I had a great experience with my ported BMS/ RP-280s and my sealed uls mk 2.
@RUreceivingMYtransmission spend as much as you can afford on good quality bass. It will pay off in the long run. Trust. I think HSU is your best bet for a quality value sub.
Also to the OP, some say this doesn't matter but after owning both front and down firing subs, I would pick front firing any day in a small room. I think you feel the bass more. It's hard to explain but there something about near field bass that is awesome. There another member here
@Danzilla31, has a PB-4000 right behind his seat
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I have a similar shaped room and I can tell you if you place both subs next to the TV a lot of the bass will get throw over to the kitchen area, which creates a whole other problem. Even, if you get two subs, I think you'll find that the bass is heavier on the left side of the room than the right side. Beware, if the bass does not sound good out of the box your gonna have to spend some time and really fiddle with sub placement. I actually had to re-arrange my entire room based around my new subs.