No difference in firmware for HL or proportional systems, the only difference in firmware is the K (plastic tracks) or M (metal tracks) version of the Booster chip. wirings for both systems are substantially different:
http://www.el-mod.de/pdf/prop_DoItYourSelf_english.pdf here are the connections for a fully proportional controlled Booster and here:
http://www.el-mod.de/pdf/booster_english.pdf for a standard HL installation.
The main difference is the wiring, when purchasing a Booster unit you must indicate plastic or metaltracks and HL or Prop in order to receive the adequate chip and wiring. When needed you can convert a Prop installation to HL or vice-versa.
Regards