As others have noted, the Aristaeus was voiced with the HE90 in mind primarily. It's going to be a really stereotypically "tubey" (warm, lush, etc.) sounding amp, especially compared to the BHSE which will sound far more transparent.
Whether the Aristaeus is appropriate for the SR-009 or not is entirely up to you. It can certainly drive the SR-009 without any technical problems, but some might feel an amp like that blunts the capabilities of the SR-009. On the other hand, some may feel the SR-009 sounds too thin and/or bright on the BHSE.
My advice would be to try to audition them in person somewhere if at all possible. Otherwise, read a variety of impressions for each amp you're interested in until you get a general idea of what it sounds like paired with the SR-009. Then go with what suits your personal tastes. There are other amps out there to consider: for example a Stax SRM-717, SRM-727 (modded), Liquid Lightning, or Electra. You can also go the DIY route and build / have built a KGSSHV. Also keep in mind your source is going to play a big role. You'll want something really nice to feed into a top-tier Stax chain.
Edit: Speaking from personal experience, I prefer the Liquid Lightning with the SR-009. I'm one of those folks who find the BHSE underwhelming with the SR-009. Others love the pairing. Personally the BHSE would be my first choice for amp with the SR-007.
Here's a good article by Tyll on a few well-known amps: http://www.innerfidelity.com/content/listening-great-headphone-amplifiers-and-stax-sr-900
The Aristaeus isn't there, which isn't surprising since [again] it's associated with the HE90 more.
