Audiophile equipment is new to me, though old(er).
For the last few years I'v been trying various speakers: Some can benefit from a sub, I believe. Currently I own Tylers Mini, Rain Makers, Silverline SR11&&17, ERA D4 and most recently a pair of Triangle 202, which I like alot.
Yes, I'm infected and probably need help. I'm therapist, which is of zero help, of course...save the humour.

I presently use an inexpensive Yamaha sub. My room is 10x12, 10 ft ceilings. Power is Harmon Kardon 3470 or NAD 7175 PE. Any suggestion for an all around good sub with flexibility for the various speakers and those to come?

Thanks in advance. Cheers.
Your room is really quite small for a sub in general. If anything, I would suggest a REL (which is one of only a few sub brands I would even consider). I used to own a pair of T3s ($250-300 used) which do well in a smaller room and stand speakers that have limited LF extension.

The reason I recommend one of these smaller RELs is that I think most of their bigger subs will overpower your room and possibly even extend too low. At your room size, my goal would be simply to extend down to about 28-32 hz. and do so with a smaller driver (8" in my mind).

I have to be honest though and suggest that you would probably be better served by stepping up to a better performing integrated amp. Since I am no expert on integrated amps, I don't feel right recommending a specific one as I have limited experience with them.
Hi Earthquake, I sold you the 202's and would highly recomend the Velodyne Optimum 8 sub-woofer. It's a sealed sub that goes flat to 27hz and rolls into the teens. It has a eq feature that sends out several soundwaves into the room, you hook a supplyed microphone to the sub and put the mic where you will be seated. The mic tells the sub what algorythems to set to make everything from 120hz to 27hz flat. It's the only sub I've heard that can keep up with the Triangle. Trust me on this one.
You need a sub-woofer with equalization, preferably one that calibrates itself. You also need a sub-woofer (or sub-woofer controller) that will put a high-pass on the main speakers.

1) Your room has its fundamental resonance at 47Hz and will have bass increasing below that. Since you're not going to buy a commercial sub-woofer that starts rolling off at that point due to its mechanical parameters you need to deal with the situation electronically to avoid excess low frequency energy.

2) Your room will have horrendous resonances at 57Hz and multiples thereof that give you one-note bass. Notch filters will fix those problems for a single seating position. A higher cross-over (try 120Hz) will move the first resonances out of the main speakers' pass-band so you only need to notch the sub-woofer output.

Forget REL sub-woofers which do neither.
That room will never be right for bass. It's lousy advice, I know, but... change the room. There's a limit to how much you can fight the physics.