Perhaps Reply-to= Both  or  Reply-to= Both,Respect  would satisfy
your disgruntled subs.  Of course, that won't solve the problem
as some mail systems don't understand the differeces betwee
From: Sender: and Reply-to: so what the subscriber sees and can
reply to automatically depends on the sub.'s system.  And of course
many people do not pay any attention to the addressing when they
do an automatic reply.

If the list is intended for discussion ON the list then certainly
the list address should be in the Reply-to: one way or another as
you won't get much discussion ON the list if it isn't.  If the list
is something else, change to suit.

Douglas