As for the INTV FB<-> INTV 2 converters, if you don't want to add that functionality, may I refer you to intelliviisonaries.com the INTV podcast, and Nurmix uses it as a store for his INTV FB-> INTV 1 and INTV FB-> INTV 2 passive controller adapters. I own a pair of INTV FB-> INTV 1 adapters, even installed them myself, and bought 3 Flashback pads, 2 for the new console, and one to pad hack or a fight stick. If you don't want to add the feature, consider it taken care of.
Unfortunately, I understand pad hacking enough to know in most consoles (North=1 AND East = 1) electronically equals NE. The 2 toughest system to deal with that problem are the 5200 and Intelllivision. With the 5200, 100% N + 100 % E = 141% NE. Only a couple games go into error when that happens, and that can be prevented with a mechanical 4/8-way switchable gate which prevents diagonals.
Intellivision requires actual processing brains because one pin does not equal one direction. Northeast is a separate actuator and not just the electronic sum of the North plus East. It would require some sort of circuit somewhere which either on the joystick, actuate another switch when the 2 cardinals are combined, or what you're doing on the Inteliivision. Since it's stupid to re-invent the wheel, I'll wait until this comes out. I may get either one Genesis and One Jaguar or 2 Genesis ones, depending on how "keypad heavy" certain Intelliivison games are. I guess it depends on what my main 2up, either my firends or my brother, want for intellivision, either a Genesis or a Jaguar.