I listened to bits of a couple of tracks. I enjoyed the tranquility and ambience.
I think there is scope for simplifying your set up, and that should make things a bit easier, specially if you are recording.
However, it does involve Reaper, so getting your head around that would be handy. Fortunately, Reaper is not that hard to master.
Firstly the connections:
1 midi out of keyboard into midi in of Roland interface.
2 midi out of interface into TG500
3 audio out of TG500 into line in on interface
4 audio out of interface into amplifier
5 USB from interface into computer.
I don't know if you are using any of the Roland E70's internal sounds. If you are, that adds another layer of complexity, but no big deal.
You can do what it looks like you've been doing, in which case:
3a audio out of TG500 into line in on E70
3b audio out of E70 into interface
Forget the line out of the computer into the amp. The way you get what's being recorded to the amp is computer > USB > interface, and from the interface's audio into the amp (step 4 above)
Secondly, recording:
I'm assuming you've got Reaper, seeing as you noted you couldn't get your head round it.
1 Open up Reaper
2 Go to Options / Preferences / Audio / Device and select the Roland capture for input AND output
3 Go to Options / Preferences / Audio / Midi devices and make sure the Roland capture is enabled for midi input and output.
The next steps set up Reaper for the Miroslav and violin
4 Create a new track (CTRL T).
5 Click on FX. This will bring up a dialog box. Click on VSTi and with luck you will see the Miroslav listed. Click on this, then on OK.
6 Click on the red button to arm the track for recording
7 Click on the down arrow where it shows the input, select "Input: MIDI", select the Roland MIDI, select channel 2.
8 Click on the little arrow below FX to enable monitoring.
Now for the midi and audio from the TG500
9 Create a new track
10 Click on the down arrow where it shows the input, select "Input: MIDI", select the Roland MIDI, select channel 1.
11 Click on I/O at the right of where you put the track name. Click on the down arrow under "Midi hardware output" and select the Roland midi. Keep the setting "Send to original channels".
12 Click on the red button to arm the track for recording
What we are doing above is grabbing the midi from the keyboard, then sending channel 2 midi back out to the TG500. Now we need to capture the audio from the TG500.
13 Create a new track
14 Click on the down arrow where it shows the input, select "Input: Stereo", select Roland audio channels 1 and 2 (or left and right, whatever it has).
15 Click on the red button to arm the track for recording
On the Roland interface, set the 'Mix' knob about half way between 'Playback' and 'Input".
With luck, if you play the keyboard, you should be able to hear both the RG500 and the Miroslav, each doing their own thing.
If you now hit Record, you will start recording three tracks. The first will be the midi for the Miroslav, the second will be the midi for the RG500, and the third will be the audio from RG500.
When you stop and playback, the recorded midi on the first track will play the Miroslav, the second will play the RG500, but you don't necessarily need this so you could mute it. The third will play the RG500's recorded audio.
This may seem complicated, but there are benefits. If you have made a mistake in playing, you can edit the MIDI and correct it.
So I am not sure how helpful this. It maybe more than you want to deal with at the moment.
MIDI, select channel 1.