Hi, I would start by thanking [PieterP] for all of his efforts on this library and maintaining a presence on forums to support users.
I have had great success making some small midi boxes and am ready to have pcbs made(exciting).
I am unable to get my head around weather it is worth trying to implement input LED for monitoring things like mute and solo. Whenever I try to experiment with the concept my brain hurts and I get nowhere.
I will try now to post the code I am using for my most recent midi tester box(no mux). It is using a leonardo R3. I have also had easy success with mux and will be using 74HC4067, on the finished device. and 74HC4051 for the 8 faders.
#include <Control_Surface.h>
USBMIDI_Interface midi;
CCPotentiometer potentiometers = {
{(A0), {MIDI_CC::Channel_Volume, CHANNEL_1}},
{(A1), {MIDI_CC::Channel_Volume, CHANNEL_2}},
{(A2), {MIDI_CC::Channel_Volume, CHANNEL_3}},
{(A3), {MIDI_CC::Channel_Volume, CHANNEL_4}},
{(A4), {MIDI_CC::Channel_Volume, CHANNEL_5}},
{(A5), {MIDI_CC::Channel_Volume, CHANNEL_6}}
};
CCButton button = {
{7,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_7}},
{8,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_1}},
{9,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_2}},
{10,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_3}},
};
CCButtonLatched button1 = {
{11,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_4}},
{12,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_5}},
{13,
{MIDI_CC::General_Purpose_Controller_5, CHANNEL_6}}
};
void setup() { Control_Surface.begin(); }
void loop() { Control_Surface.loop(); }
The part I am struggling with the most is mapping the inputs(to the midi controller) as I believe you can not just map the DAW outputs with the same ease that you can map the inputs(inside the DAW, just open the midi learn function turn a knob or push a button then press ok). And that you would need to implement something like the MCU mapping.
I can see that there are commands like "button:MCU,CHANNEL_1" But I am not really getting it, when it comes to LED. 
I changed the midi device in Ableton settings to be mackie classic, and I can see that there are midi messages being sent to and received by the leonardo.
I am probably happy to have a midi controller with no LED feedback, but if it is possible to implement with relative ease, then I would hate to leave such useful functionality on the table.
My apologies for being such a noob and thankyou in advance for any help anyone could provide with making this design decision.