Replying to wasn't the focus, but of course, options could be "to sender"  or "no replies" or to the "sent-to group" only.
subgroups seem too clunky/restrictive to simply send msgs to admins or the like.

For example, for whatever reason say a group has 4 lists (sometimes members changing), admins, renters, buyers, tire-kickers. 
A SG for each is not useful because it involved subscribing/unsubscribing, and there could be cross-listing (there could be two (but not the same) admins on each list, or there could be plain old members on 2 out of the 4 lists, and 2 on another list, and so on.

thx
K