I had large 3-way speakers with transmission line bass years ago (I. M. Fried Model Ms) that overloaded every room in my house I tried with bass. But they were magnificant a 160 seat chapel with a 20 watt per channel amplifier.
I currently run floorstanding single driver transmission line speakers (design ala Martin King) that use an 8 inch driver in a 13 ft x 21 ft x 8 ft room. Speaker/listener setup is nearfield as per Cardias and I have (6) 2 ft x 4 ft absorption panels at front corners, first front wall reflection points, and first side wall reflection points. This set up works the bass much better, however on some selections I've noticed a slight bass frequency extension with the door to the room open. Note that the room is insulated from the rest of the house, so I normally have the door closed.
Some good advice here so far:
If you follow the Cardias formulas, the speakers would be about 5 feet from the back wall and 3 feet from the side walls. This gives a good balance between nearfield room gain and space for soundstaging. I've found that the listening position is less important and primarily comes down to listening preferences (nearfield or not).
Next priority should be room treatment. In my Cardias prescribed rectangular room and speaker/listener locations the advantages of the absorption panels is minimal. This is probably due to room friendly TL bass roll off, following the Cardias methods, and the severe "beaming" of high frequencies due to the large single driver (which BTW is rated up to 20,000 Hz on axis).
Lastly would come room equalization, as it can only be applied to a single spot in the room, so it should be considered the bandage to the sores.
Unless you're listening at very high sound pressure levels and/or using a very low powered amp, increasing the amp size shouldn't make a difference. However keep in mind that tube amps typically have very poor damping factors meaning that they can produce uncontrolled, loose, flabby, exagerated bass (especially deep bass).
