Pre out main in splitting?Maybe a quot;well duh quot; Q

Sure you can use an adapter as mentioned. However, unless your equipment is strictly bargain-basement level, you'll want to use quality hardware for best sonic performance. A search of the forum archives yields 4 threads containing multiple posts on the subject of y-adapters. Follow this link for further information:
http://audiogo5.iserver.net/cgi-bin/fr_srch.pl?&1&procsrch&3&4&

The splitter will not cause any load problems to either amp and you can do exactly what you want. I have had many customers do this over the years without any issues.