Hi,
Not sure if you've already made your final decision, but in any case you might want to look at the AEA Listening Room for further research. There you will find a selection of sound samples of AEA's mics and preamps:
AEA Listening Room
If you're into the API 500 series gear at all, I'd highly recommend checking out the
AEA RPQ500 preamp. Super transparent and in a similar sonic league as Grace and Millennia gear, but with more gain, the built-in eq, and a lower price point!
Pretty much a no-brainer!
Cheers,
Julian