Sorry for not replying sooner guys, i've been really busy. Most of the circuit is still sitting on my desk right in front of my monitor! I havn't forgotten about it! Just been busy dealing with a lot of crap lately. But that's life i guess.
I did look into what units it will support with wires. Now, not every head unit in these brands support them, but i'm fairly sure most do support the hard wire control.
Brands include:
Alpine
Clarion
Eclipse
and Sony
I'm not aware of any others yet, but they may do.