Why not use a PC style UPS?

Most power conditioning systems found for Home Theater seem to be quite pricey. I am most likely very naive to the technical aspects, but it seems to me that a much less costly alternative could be found mated to your computer... an active UPS. Just wondering what I am missing. Thanks in advance for your assistance and insight.

They generate large amounts of electric noise. They are typically designed as surge protections and UPS, not power conditioners.
been there & done that,onhwy61 is right about the noise level,you would not be happy with the results,i wasnt.
What Onhwy61 said
You could ruin your gear. Some UPS only produce a "Square wave" electrical signal. Cheaper to make. Computers don't care. You need a good sine wave otherwise your gear may suffer damage.

APC (American Power Conversion) who is one of the largest makers of computer UPS devices is coming out with a Home Theater and Audio line of UPS gear. They had them at CES. They should be available in the spring.. See the link below..

Computer UPS's aren't designed for high current transients (such as you would get from an amplifier). That's why you don't connect laser printers to a UPS. It might actually damage the UPS.

I just picked up one of the APC units Sugarbrie is talking about, the A15 yesterday. It replaced a Powervar and I'll not go back. I am most impressed with the performance. It has isolated filter banks for "Video" (TV & VCR), "High Current" (Amps & Subs), "Digital" (all the rest), 3 sets of coax, phone jacks (1 in, 2 out), IEC (with what appears to be a 12ga 8ft power cord). After setting it upand powering up, I thought my Sony Wega 35in CRT was almost an HD, the audio sounded more coherent and the blue lit front of the A15 is just plain cool. Oh, I forgot to mention that it provides adjustable Voltage Regulation. The surge protection seems to be second to none and is fully guaranteed. I'm quite happy with it.
As long as it is a high quality online UPS, meaning it runs off of the DC battery with an inverter, with true sign wave output you will be fine. The Liebert models come to mind. Do not load it over 50% of the rated capacity otherwise you won't be able to handle high current components. So on a 20A model keep you load to 10A or below.

With the exception of online UPS models, UPS's do not hangle surge supression well at all. That is marketing hype. Get a separate surge supressor. It will do a world of good in most cities unless you have exceptionally clean power. Brickwall is good for the money.