Nothing extra is required, other than awareness of the bajillion voltage standards.
ES-3 expects your computer to output things in +/- 1.0 range.
ES-6 takes in +/- 10V from the modular and converts it to the +/- 1.0 range.
ES-8 follows suit.
BEAP does everything in the +/- 5.0 range (maybe 10.0?), as it expects to interface directly with your audio interface without scaling. If you use the BEAP output module, it converts everything to an ES-3 safe value. You'll also want to scale (boost) messages from the ES-6 for the BEAP range. They may have changed that, but it was like that the last time I checked.
Euromax does everything in +/- 1.0. It can be connected directly to an ES-3/6 or 8 without scaling. However, Euromax was written by a newbie grad student in Max 5, so there are tons of bugs.
Euro Reakt (for Reaktor) can also interface directly to an ES-3/6 or 8 without scaling.
Regular Max/MSP (i.e. not BEAP) does everything in whatever range you tell it. Most of the MSP objects expect a signal in the +/- 1.0 range, so they'll connect directly to ES-3/6 or 8 without scaling.