I used the Eris master root application, downloaded the official Rom from there. Let me know what you are looking for, like kernal or whatnot
I haven't used EMA, so I don't know what choices of ROMs it gives you. If one of them is Ivanmmj's "Official 1.0 OC" (or maybe "Official 1.0 alpha"), that's a decent ROM.
As far as Astro goes, the version of the rooted ROM underneath it won't really change whether or not it can operate in root-enabled fashion or not. I'm not an Astro user, so maybe some of the other Astro users with root can chime in here (whether it can work in a root-enabled fashion or not). I did find one comment on this site (in the Apps section), where the reviewer said something like "Astro is the very best ... until you have root".
If you don't mind shelling out UK 1.99 (US $3) for Root Explorer, just use that.
If you want free, you can use "adb pull", "adb push", and "adb install". Kind of clunky, but they work. Note that adb will pull entire directories, too, for instance if you do something like
adb root
mkdir appbackup
mkdir appbackup\system
mkdir appbackup\market
adb pull /system/app appbackup/system
adb pull /data/app appbackup/market
that will copy all your apps to the PC - if you have root.