On the R-09, "8" on the volume was the unity setting, so I never changed levels... but with the R-09HR, I have not seen 100% confirmation of a unity setting or a "go for it use anything" setting
Was there a 100% confirmation of a unity setting or a "go for it use anything" setting for the R-09? `8` was a myth.
Level 8 on the R-09 line in maps,in my sheets, to about 9 dBU or 2.18Vrms or 6.18Vpp. (all 30 + mute level settings got an interpolated -13 to 16 dBU figure)
The default level is 0 dBU or about 2Vpp, closer to normal consumer line working levels.
For the HR the spec says:
Line input: 2 dBu (Default input level)
This is very close to where the codec chip has it's 0dBFS point, according to the data sheet.
Have a look at the codec (made by WM) datasheet. Map the level settings to the levels that the chip supports.