When using the receiver's amp section you must use what the manual tells you to use. When it comes to using an external amplifier as long as you use the appropriate pre-out, you can plug that sucker into whatever you want on the amp. L/R/C/SR/SL doesn't matter so long as the speaker wire is connected to the matching binding posts.
The receiver should be outputting sound through the pre-outs and the binding posts, so hypothetically it's possible, but you just have to make sure you aren't outputting surround sound to the FW/FH speakers or vice versa. For instance, if I was using the FW/FH pre outs on my 3009, I could also connect a pair of speakers to the FW/FH binding posts on the amp and I'd have 4 speakers outputting the same signal. However, your situation is a little different since one pair of pre-outs is labeled as all three. The issue is, if your receiver isn't meant to output 9 channels of audio, then you may only be able to pick one or the other for both the binding posts and the pre outs to output.
Which receiver are you trying this with?