Captured the IR for the "Back" button and hooked up with existing settings from your TiVo V6 Set top box device already in the app. I put this into a custom device JSON (imported via Admin>Brands etc) to test it was working and hooray, it works!
The relevant portion from my device JSON for you:
{
"label": "BACK",
"code": "0000,006D,0009,0000,0023,001F,0045,001E,0023,0041,0045,0041,0045,0041,0044,0020,0023,001F,0023,0042,0044,0D85",
"protocol": "PRONTO"
}
If you could include that with the TiVo V6 set top box device config in the next release then that would be great @jason