the EMS 6 is the one with the dial so your can quickly retard the ingnition (the EMS5 does have this) i believe its more gear toward n20.

the EMS5 is a more complete solution allowing you to advance the ignition as required and then retard it were you want, which is idealy only at peak torque which i'm 95% you can do with the EMS5. I doubt the TT dizzy module readvances the ignition past peak torque.

also the EMS5 is more expensive, i have a feeling the EMS6 works better with EFI, Cavs runs on on that DIY 2.8 twin turbo EFI 4i.

do you have one or are your getting one? i'd seriously look at the OMEX150 mapple ignition system this uses a phase sensor and MAP sensor. okay its more expensive but should be far supirior to the MD kit, couple that with an MF2 and you'll be cooking on gas. I bet karl or someone would be able to sort the OMEX gear out he certainly does the MF2 as you know.