I have tried both, and with bad results for the FireXon (on Lion that was). The 610 on the other side works perfectly well. It doesn't shield well for noice, and the gain pots caused some crackels, but it worked perfectly fine. With my somewhat limited ears I could not find anything to complain over for the audio quality either.
My general rule for iCON btw. would be to stay away. I got a whole home studio pack in return for a favor to my local music shop because the norwegian supplyer cut the brand. And I must say Im pretty dissapointed with the lot. The only somewhat decent thing i got is the ReoTube preamps. (I never got response from the support either, when asking for working OSX drivers)
But if youre looking in this price range you should definatley consither the TC Electronic Desktop Konnekt 6. You only get noe preamp, but a good one. And you would probably want to do vocals and guitars I seperate takes anyway. (To prevent bleeds, get more steady tracks, and so on) It has a stereo 1/4" instrument input also, but don't go there. Use a mic on the guitar if youve got one.
Good luck