I'd look at a bookshelf sized pro-audio studio monitor made by Hafler called the M5. You can listen to them at most Guitar Centers. They retail for around $220 a pair I think. I own 5 of them and they seem to effortlessly outperform most bookshelf sized monitors at many times the price tag.
I have been listening to my music, movies, t.v., vinyl and old VHS tapes in PLII for almost 2 years now. I have a pre/pro that allows me to select many different surround modes, all channel stereo and conventional 2 ch. stereo. I must say that I prefer PLII to any steering logic matrix or...
www.decware.com has a really neat design for DIY electrostatic computer speakers. Cost is very minimal and the design looks pretty cool. All materials can be picked up at the local hardware store.
Another thought. You can use kitty hair, matting and resin to fiberglass the complete interior of the enclosure. This will displace very little as the thickness only needs to be a 1/16-1/8" and will add considerable strength to the enclosure. It is a great way to fully seal the enclosure as MDF...
You can weld the angle iron to pieces of 5" x 5" plate. these plates (on either end of the angle iron) can be mounted to the enclosure. I personally like to use cylindrical piping due to its' strength.