Uing two a/d interfaces

Hi guys. Most of my stuff is done in midi using outboard sound modules - with a few VST's for good measure. So I'm not so good when it comes to audio stuff! However, I have a project with a female vocalist and we have both been impressed by the capabilities of Roland VP-7 and are thinking of using it. However, as this is an outboard audio FX box it would mean the recorded audio (using my firewire 410) being routed out of HS6 into the VP-7 and back in again - presumably on another track . Can I do this in HS6 without causing "digital feedback"? Since I have another interface ( an Emu 0404) sitting idle, I thought maybe I might need to keep the effected audio separate and use the Emu get the output of the VP-7 back into HS6. Am I on the right track here or am I getting into a "senior moment" muddle. They do happen occasionally!