As an example, when you say Studio One uses 5-10% cpu when you open an empty song with no tracks, I can confirm that here (at 64k with ASIO4ALL), peaking about 7% on it's cpu meter (looks like it's just core 1 to me), but ... this confirmation is on a White MacBook core duo P7350 @ 2ghz, not exactly what I'd call a powerhouse system by any stretch. I don't see anything like that on my Win 7 desktop system.
So if your 4-core (?) desktop powerhouse (?) is kinda performing with Studio One like my not so new or not so powerful 2 core older White MacBook, that's a little surprising, and I understand why you're not all that happy with that.
![Sad :(](./images/smilies/icon_sad.gif)
Anyway, my desktop system is an off-the shelf Gateway "gaming system" that I paid $950 for. I never even turn Norton AV off on it. 8 cores, it performs pretty well.