need help with 5 channel amp

I have paradigm studio 100s and I am in desperate need of an amp. I am looking at the Parasound 2205, anthem mca5, ATI 1505, and the outlaw amp. I am on a budget and will buy used. The ATI worries me because it only has 150 watts and I think I will need more power then that. I am sure the parasound is the best but it also is the most expensive and I would have to buy it used. Also I liston to 2 channel music a lot so which one of these amps would be best for that. What would you all choose.
Regardless of your budget, I'd buy used - all the models you mention are fairly readily available used and you'll save a lot of money. Certainly, the Parasound and the ATI have been very well reviewed. I haven't listened to any, but from what I've read about them, I'd first investigate the Parasound. If you're interested in the ATI, they make a 250 w/ch version as well which is also regularly available used.
What kind of a budget, if you don't mind? 1K, 5K? You can get some pretty good used stuff for cheap. If you are considering Parasound, you might try Acurus as well. They make a 125x5, but they also have a 200x3 and a 200x2. Good clean power for not a lot of money.
my budget is around 1500 tops
Go with a used Parasound or Acurus. Both make a 5 channel. I've seen the Acurus used for $1250. I haven't looked at Paradigm speakers for several years, but if I remember correctly they are fairly easy to drive. Are you sure you need more than 150 watts--or even that much? Both the Parasound and the Acurus pack a pretty big punch. You might audition these amps new in a store with some comperable speakers to help you zero in on the one you like. Good luck.
I use the Anthem MCA 5 in my home theater setup. It has 200 x 5. The new mkii version can be had new for about $1000. There is even an add on this site for them. I have been happy with the sound of it.
When I was looking, it came down to two the ATI 1505 and the Sunfire Cinema Grande. The ATI was just as strong as the Sunfire in all regards. I was leaning towards the ATI until I found a Sunfire for $1250. So I have a Sunfire Cinema Grande and have been pleased with it but, IMHO I would have been happy either way. Classe also makes a very nice 5 channel that would easily compare to the ones you have been naming. Earthquake Cinenova has been highly reviewed also. Hope that helps, good luck.
In regards to your concern about power, I drove Studio 100s in a surround setup for about a year with a Proceed Amp-5. At 125 watts per channel, the 100s could be driven to quite loud listening levels. Unless your room is quite large, the 100s at 89 dB sensitivity should provide fairly enjoyable volumes with a 150 watt/channel amp.

My opinion, for what it's worth.
Hi: You didn't indicate how much money you have to spend, beyond saying that you are on a budget and will buy used. If your budget will stretch to buy a used Bryston 9B-ST, it is one of the best 5-channel amps being manufactured (rated "Class A" by Stereophile mag, and "State of the Art" by at least one major HT mag). The dealer where I bought my Bryston 4B-ST and 5B-ST will sell a new 9B-ST, with full 20-year warranty, for about $2800 (which is about what you'll pay someone for a used unit).