audio interface?

[ekurburski]

I have seen in a couple of advertisements that the perform-vx can be used as a audio interface with 4 in and 8 out,  I see no documentation on this.  So what I want to do is run a vst live from another keyboard while playing background on my 3000.  I have a PSR740 I'm not using for anything at the present time.  I also have several DAW's and several V ST's. 
I would rather not have to purchase a additional interface if what I have will work. Any ideas and comments would be most appreciated.

Also I got the harmonizer used from Don Mason.  Do I need to register it with tc helicon?