I managed to do this by using a LineSelector from Boss. Since I see many people asking about this, I will dare to open an specific thread for this.  Here is a layout of the connections:


By alwalt at 2009-09-09

The main idea is to use the EF86 loop as a send/return path. From the TopBoost loop  only use the send signal. This send is mixed then with the EF86 send (via LS2). The both mixed signals -dry go to the effect chain. At last, from the output of the effect chain the mixed effected signal returns to the EF86 Return of the effects loop.

Since the LS2 has a level adjust for each channel, it allows to level the effected signal to prevent volume loss.

I have tested it on band practice and it's working fine. I hope it could help people who wants to share effects on the loops of the DC30...