Keep in mind the AD-20 will not pass a 24 bit signal, so you'd be stuck with a 16 bit recording, which is fine, but if your going to do that and stealthing/overheating is not an issue i'd go with the jb3 as its much cheaper still than a MT.
Now I would also use a mp-2, these have gone for around $350, with mixpre's for about $450, however they are in short supply. Then if you have some extra cash pick up an SBM-1. You'll then have meters and a nice A/D (at least nicer than an A/D-20). Although I haven't used an external A/D in a year with my mixpre and i love the sound of the shows.