In the event that I get hold of another D1500 am I correct in thinking that my best option is running them off the DSP33's and getting the 568 to treat the set up as 5.0 for movies? There was a similar thread about a 7.1 system last year but it didn't seem to be resolved.
Unless there is a very good sonic reason for not doing it I plan on the subs being directly below the DSP33's, which would be around 8' apart.

568.2mm, DSP6000, DSP5200HC, DSP33 rears, HD621, LG G3, Sony UBPX800-M2, F80.