Several very good questions. First, 16 feet, your longest dimension is roughly 38Hz (1/2 wavelength). You can not get even 1/2 of a 25 Hz wavelength in this room. However, this does not mean you can't play notes at that frequency in the room. Notes below 38Hz will be reproduced, but as pressure rather than (I'll call it) free flowing waves. This is similar to what happens in a car or headphones. You aren't going to have that low organ rush (like a wave of sound going by you) of pressure that you do in the Cathedral, but if your speakers are up to it, you will reproduce sound pressure at that frequency. So don't be overly concerned about the room dimensions. The next problem is standing waves. You may have heard of the Golden Triangle. If you have not, try to get a copy of Stereophile Guide to Home Theater Issue 23, March/April 1999. It discusses this principle in length. Your dimensions are close, but not perfect. You can alter one of your dimensions, or you can do as you suggested and slightly taper the walls. Be sure to taper your back wall as well, the 16 foot length will give you the biggest problem if it is not addressed. There are other ways to combat the standing wave problem and that is to build bass traps into the walls. In this way you don't have to taper the walls, but it requires patience in tuning the traps once you are done. If you are interested in this route you can e-mail me and I will give you more information on how to do this. Last item is the floor. I'm assuming, since it's a basement that it is concrete. I had the same situtation and used a floating floor of wood laminant. I then used an area oriental rug for sound absorption. I like the near field reflection off the floor in my room. However, there is one big difference--my ceiling height is 11 feet. I don't think I would recommend a hard surface floor with a low ceiling. High density natural fiber carpet is probably your best bet. You will also need some absorbers and possibly diffusers, but you can deal with those once the room is built unless you want to build them into panels on the wall. Asthetically, that can be very nice, but from cost standpoint it's probably not necessary. Sonex or other panels for first order reflections work very well and can moved to the correct location if you move your speakers and/or listening position. Lastly, I would like to point out a book that can answer your questions in far more detail than I can in a post: Master Handbook of Acoustics. It's available from Amazon. I have ordered a new software package for room evaluation, that allows for non-parallel walls. I have not received it yet, so I really can't tell you how well it works, but it looks promising. The software can be found at: http://www.cara.de/ENU/index.html. Hope all this helps, and good luck.