Sadly cc#64 and cc#65 are NOT mute and solo controls.

Admittedly some DAW software may use them for this function, but that is a non-standard use, it is not their assigned attribute according to the MIDI specification.

According to the MIDI spec. CC#64 is the foot control "sustain" sometimes referred to as the loud pedal.

Again, according to the MIDI spec. CC#65 is the control to turn "portamento" on and off.

I doubt that ARIA will implement the non-standard use of important controls such as these, especially as cc#64 is already used for legato on/off (similar function to sustain) in many instruments. (It uses cc#68 (correctly) in the notation version of the libraries.)

But I'm just a Garritan library user like you.

OK, it doesn't have to be CC#64&65, it can be any available CC#s since midi controllers can be programmed.  The idea is that it allows "pulling" or "pushing"  organ stops on the fly in standalone mode. 

Aria Player does not allow for program change and is a real weakness for standalone performance that I believe is easily solved by incorporating this feature. 

I've always wanted this for the same reason (to build organ stop like arrangements with the Classic Pipe Organs Library).

With some advanced controllers it's possible to emulate this behavior to some degree by simply sending master volume changes of CC7.  The catch there is that you'd still use processing power for the voices set to 0 volume, and unless you've got a really advanced controller (or some software in between) there's no way to remember your last volume setting.

I just bit the bullet and got Bidule which allows me to build my own MIDI filters and such as needed.

I've also created a kind of Organ Stop Emulation for CuBase using 'generic remote maps' to simple toggle the monitor or record buttons on each track on/off using the MPC Pads on my MPK2.