Actually I've had 2 different API 2500 units in here (first was a demo unit) & both sounded different from each other unless they have a run in time.
As for your comments regarding the 'sound' of Ye-Old mode. I usually use it with a Med thrust like you guys as usually I like to let the low end through the compressor unscathed. Where I hear a slight build up is circa 150-200Hz. Don't you think it sounds fatter in the low mids in Old mode? That is often the appeal of Old mode for me, that along with the slightly more gentle slower action of the compression. Even with the Med thrust I still hear more high frequency around 10kHz compared with the New mode with my unit. While the New mode is a little more aggressive, I prefer to use it where the needles are barely moving longer attack & release settings & either in Hard/Med/New or Med/Med/New modes if the kick drum is poking through too much I put it in normal mode which is still punchy yet adds a nice control to the low end.
There is no hard & fast rules, I used to think Hard/Med/Old was the way to go but my instincts react differently now based on the mix/genre & what I want to achieve. Don't rule out the other modes, it's worth playing around with this thing.
As for the Phoenix, the Mastering Edition is a different beast to the non-ME version. The drive is far more subtle & honestly I don't think the ME version sounds very tubey at all. The other benefit of the ME version is the S.C. filters. Most of the time I've got it set on one particular setting & master into it & the only thing I tend to change from time to time is the S.C. filter setting.
Matt