Need advice for Nanosat 5.1 Subwoofer Replacement

This is my first post and I'll try not to waste anybody's time.

The subwoofer that came with my Nanosat 5.1 system needs to be replaced. It has the constant loud humming that it seems is normal for this model when it's several years old. I've gone through extensive troubleshooting and it's definitely toast.

I read the sticky post on how to ask this question so here are the details.

My budget is $400 or less not including shipping and taxes, preferably less.
The Nanosat subwoofer form factor is nice but I have room to go a little larger if necessary.
The room is 13'x21'.
It will be used for 80% HT/TV viewing, 10% music and 10% gaming.
I occasionally listen to music at louder volumes and I definitely like to "feel" my movies but I'm not willing to give up sound clarity for extra thump.
I would prefer a nice looking cabinet but it will be fairly hidden.
I'd like to replace it as soon as possible but I"m willing to wait to get better quality.
I'll be powering it with a Denon AVR 2808CI receiver.

Thanks in advance.

Thanks for the reply. I've decided to pony up the extra money for a SVS sub. Now I have to decide which one would be best for my front room. The exact measurements is 1968 cubic feet. The problem is that the room is not sealed. It has a doorway sized opening to the kitchen and a 6.5'x7' opening to the dining room. The kitchen and dining room combined are twice the size of the front room.

I'm not sure the SB-1000 would be the best choice given how much open space I have. It definitely won't be able to pressurize the room.

Any thoughts?

Just the Nanoset. Thanks for your help. I'll order a PB-1000 later today.

Thanks cel4154 for all of your help. The new PB-1000 is awesome and a huge improvement over the Mirage S8.