Hi, long time no post... There appear to be a raft of fairly inexpensive digital to analogue converters available (mainly sold to convert from digital TV to analogue hi-fi equipment). Most offer TOSLINK and SPDIF. I want to try and maximise the inputs to my Scarlett 18i6 by using the L&R outputs from my Peavey PV6 mixer into the SPDIF of the Scarlett. I've contacted a couple of sellers on Amazon to see if their converters do digital to analogue and the reverse but have had no response. Anyone out there know if this is possible? and of a suitable (cheapish) product? PS I've only just bought the 18i6 so can't afford a Focusrite OctoPre or equivalent.

http://www.sweetwater.com/c796--AD_DA_Converters

One of those cheapo converters should work for connecting the unbalanced RCA tape outs of your PV6 into the Scarlett's S/PDIF in, with the Scarlet set as digital clock master. Use a 75 Ohm coax cable for the S/PDIF connection (a cable with yellow or orange molded RCA plugs, not one with red or white ends like used for the analog audio connections). 

If you want to send the balanced main outs from your PV6 to the Scarlett, you should really use an A-to-D converter with balanced inputs, and balanced cables.