13' x 9' room big enough?

IMHO, If I had to build a system for listening in a similar size room I would go for a high quality source, a good tube headphone amp and the most comfortable headphones I could afford to buy.

Perfect room for minimonitors.

Perfect room for monitors + subwoofer. Monitors can be placed per Cardas or AudioPhysic for imaging and subwoofer placed to load the room with bass. I have a slightly smaller room and the sound is outstanding.

I actually think smaller can be better with rooms because you need less power, which means you can buy better quality.

Absolutely, if you don't have the speakers yet, go for some that are not too picky about placement (Dynaudio, Audio Physics, most good monitors). Stay clear of dipoles, bipoles and time alligned (Thiel) as they like the listener further out (over 8 feet). Set up for near field listening and you will have good results (Cardas's web site has a nice formula for rectangular rooms).
I am very happy in my 15 by 10 room (Dynaudio Contours 1.8 II), which my ceilings where as high as yours though...

Very interesting suggestions, never tried a setup in a small room with subwoofer. What do you guys think about a REL Q 150 or 200, is this the way to go?