Several thoughts as I’ve recently done a bit of research on subs:
- REL makes good subs but do not have a monopoly on naturally integrating into a system. Any good, properly-positioned and dialed-in sub will integrate seamlessly.
- You should seriously consider adding a second sub especially to your 2-channel system. Two subs can provide substantial benefits over just one and three or four even more so. But two subs should be considered a minimum as it’s such an improvement over a single sub.
- Placing a sub between the speakers is very rarely the best place to get optimal in-room performance from a subwoofer, so having to place the sub elsewhere could very well work to your benefit especially if you do some basic homework on optimal sub placement (I can provide some helpful links if desired). This is even more important for your 2-channel system if you haven’t already addressed this.
- For your HT system I’d recommend SVS subs for several reasons. They offer good performance and high value as they sell direct, include a very helpful app to make integration much easier, have excellent customer support, and they offer a 45-day, risk-free trial including shipping both ways. I’d recommend two SB1000 Pro subs as they’re small/inexpensive yet still get you to an honest 20Hz, but if you’re constrained to one sub an SB2000 or SB3000 will still provide a very satisfying HT experience for relatively not much $$$. Rhythmik subs are even a bit better but are a little more expensive and don’t have the convenient setup software that SVS offers.
Hope this helps, and best of luck.