Subwoofer for music only ?

I've been using a pair of older (bought used) RELs for years...a Q150e (10" front firing 150 watts), and a Q108MK2 (8" down firing 100 watts). They work absolutely perfectly and cost around 200 bucks each. These RELs seem to have more adjustability than new ones. In any case they are extremely "musical" in the sense that they just disappear into the music, and help keep standing waves from mucking up the situation. 

Awww long-time Rel owner, I would also recommend the T5x or T7x models. 
plenty of low end extension and very well-controlled drivers. 

You can reach out to REL and they will give you a recommendation. Just be aware that any listening position that’s against a wall is going to be prone to standing waves where bass may sound elevated/bloated. 

As someone has recommended a Kef Kc62, I'd add that I have recently added a Kef Kc62 to a small room (10 x 10ft), complementing Kef Ls50W speakers (on isoacoustic stands).  I'm extremely pleased with them and use them mainly for 2 channel listening.  The Kc62 disappears completely and adds significant depth and dimension to the Ls50's (which were quite good on their own).  The small size of the Kef is a real plus in a small room.  In a larger room (with larger speakers) I have a REL S510, with which I am also extremely pleased.  That REL would be too much in size and sound for my small room.  I had considered the T7i as well, but the Kef Kc 62/s exceeded my expectations.  I would add that if you watch Best Buy's website, as well as Crutchfield's, they often have "scratch and dent" or open box models which make them more competitive price wise again SVS.  In both my systems the subwoofers provided a huge upgrade.  So go for it!!

Thanks for all the input, It's appreciated.