I just finished iPAD music station project. My goals are 1) making iPAD as EWI midi controller for various hardware synthesizers , 2) using iPAD synthesizer apps for EWI, 3) all hardware instruments can run by the USB battery bank.
I put a audio interface, USB hub, midi interfaces and a high power USB battery bank into one square enclosure. I attached a Korg NTS-1 as a hardware synthesizer as well as effect processor. For analog synths, I use a Korg Volca Keys which is modified to have a midi output. Therefore, I can use NTS-1 and Volca Keys as external midi keyboard and controller for iPAD synthesizers.
The project is very successful and I am very happy about the outcome . Now even I can connect my RME fireface UCX with ADA extension into my iPAD via USB and have 18 channels audio inputs for playing and recording on my iPAD.
The final specification is as follows;
1) Audio input : default 2 channels. can add extra audio input by Apogee JAM interface, USB microphone.
2) MIDI : 2 ins and 2 outs, can add extra USB midi interfaces
3) Number of USB ports : 4
4) DC Powerouts for external devices : 3 ports . These powers up various synthesizers by Ripcords USB-DC power cables
To use EWI to control various hardware and software synthesizers, you need midi mapping tools. Midiflow is an excellent ios app for this purpose. I found Korg Gadget 2 is a good platform for midi recording, EWI playing for hardware synths.
All-in-One Carrying Case
Parts
Update 09/2021
Finally I set my iPAD music station with Dreadbox Typhon.