In the AE environment, you MUST constrain signals to a 0 to +5V scale. It's just how the system works, probably due to part of its origins being in Stanley Lunetta's design work. Now, to get signals in and out, that's what the 4I/O modules are for...they do all of the voltage voodoo. But if you want proper scaling, that will require the MASTER and its MIDI interfacing, since the AE also isn't exactly 1V/8va.
There's also a second solution, especially for CV/gate/trig signals, and that's Soundmachines' Nanobridge. That was designed for their Nanosynth...again, some Lunetta ideas in there...and costs a whopping $40! w00t! This provides 14 channels of bidirectional I/O for control signals (primarily) and when you use the AE's +5 and GND as its references, it will autoconstrain things to the proper range.
I use all of these, btw...pitch CVs via the pair of MASTERs, audio I/O via a pair of 4I/Os, and a Nanobridge for all of the other stuff. I can also drive my AE system via Ableton's CV Tools thru a used/cheap MOTU 828FW mkii ($120 on Reverb), which is capable of dealing with the voltage scaling issue and can give me eight simultaneous channels of scaled CVs if I should need that.
EDIT: You (and others looking at the AE, of course) might find even more answers over at their forum, which you can access via their site at https://www.tangiblewaves.com/ Lots of knowledge flying around there, including some tasty DIY action (company-encouraged, even!).