Well, I don't know exactly what the gain is on the SP-9 phono stage, but if it's too low, you could always get a step up transformer for it. The DL103 is low output.
I have just done some looking around at some sites that had the Project 6.1 on them, and some of them showed the Denon DL103 on the TT. So maybe the arm will handle it. From the looks of the arm, it is a pretty sturdy looking unit. I was thinking of the lower Project TT's which had some pretty lightweight looking arms on them. The 6.1 just may do alright with a Denon. I'd recommend the DL103R in this case, because it is a better sounding cartridge than the regular DL103. Give it a try, I think you'll love it.
I have just done some looking around at some sites that had the Project 6.1 on them, and some of them showed the Denon DL103 on the TT. So maybe the arm will handle it. From the looks of the arm, it is a pretty sturdy looking unit. I was thinking of the lower Project TT's which had some pretty lightweight looking arms on them. The 6.1 just may do alright with a Denon. I'd recommend the DL103R in this case, because it is a better sounding cartridge than the regular DL103. Give it a try, I think you'll love it.