This is great... asterisk guys answering on the FreeSWITCH forums ;-) Thanks John!
That said... It's been my very personal experience, that everything i've wanted to do with asterisk i could do with FreeSWITCH. And there have been many times i've wanted to do things with asterisk and couldn't... but FreeSWITCH has native support for them. TLS is a big one for me... and, at this point in time, i could wait until 1.6 is considered "stable".. but it was months ago that i was making this decision. To the best of my knowledge, TLS (and even TCP) support in asterisk is an afterthought that wasn't addressed until recently.
Anyway, back to the topic at hand... FreeSWITCH makes an excellent PBX without the need of a proxy (and i'm sure, i don't "suspect") and will let you have complete control over the media and what happens with it.
A couple of articles for your viewing pleasure :-)
(this last one isn't really pertinent to your current investigation, just something i like to share.... FOSS working together for the "greater good")