If you wish to retain the Taigen controller (Multi Function Unit/ RX + transmitter TX) then your options are limited. If you're happy to use a soldering iron to attach just three wires to a circuit board, then you could consider
this upgrade from Beier:
http://www.beier-electronic.de/modellba ... m-hl-2.php
It's not cheap, but does produce impressive proportional sounds. This card has one or two fans on this forum, in fact....and it's worth checking the Forum archives out for more information. Beyond that, you're looking at buying new MFU (Clark, IBU2/3, Asp, etc..); together with a new transmitter and a matching
receiver- probably the 6-channel type you'd wished to avoid.
"Get your facts first, and then you can distort them as much as you please"- Mark Twain.