Help choosing Power Conditioner


Completely new to this area. I would like a unit that:
a) regulates power, keeping it within the 120v range.
b) provides good and long-lasting surge protection
c) can be used with a power amp as well as preamp, and sources all together
d) Hopefully helps the audio, making it more open and dynamic without negative effects.

I need to say under about $750 used. My candidates are:
Monster HTPS7000
Monster AVS2000 (how are these two different)?
PS Audio Power Director 3.5
Blue Circle MR1200 Music Ring
Any others...
Thanks!
kck
Keep in mind that you could encounter a buzzing or humming transformer those PowerVar or Oneac units depending on their condition and also if there's any DC present in your power delivery.
Here a link to an excellent paper explaining the conditions that cause transformers to become noisy:

http://www.plitron.com/PDF/AES.PDF
TVAD,

No dig on your post at all, I was commenting on the exchange between Snofun3 and Dedicatedaudio. I guess I was too general. I like when folks point out listings in posts, just nice to know if they have more then a passing interest in the transaction. Sorry for any confusion.
Post removed 
I must have gotten my Powervar from the same guy as you Tvad. These things are the real deal and at 229 so much cheaper than other iso-transformers out there. I have no hum issues at all.
Mike