Import a professionally mastered commercial release of music that is like the music you want to produce. Play it back. How loud is it?
Also, how are things set?..:
You’re saying yo’re leaving the Yamaha speakers at +4, right? It seems to me that it’s really an amp circuit rather than a clean switch between ‘professional +4 and consumer -10’. Essentially turning the knob right towards -10 either increases the gain of the internal amp or lowers its attenuation (same thing to you basically). So this is one point in the signal chain where you can adjust the level outside of Cubase.
For the UR22; it seems as a good time to point out that since this is engineering stuff you’re talking about you need to be specific. You really can’t just say “the knob on the audio interface” when there’s 5 knobs on the front panel… which we wouldn’t know without looking it up. There’s the “mix” knob and the “output” knob. If you set the “mix” knob to straight up you’ll be lowering the output I think. So, you should probably have that all the way up, meaning 100% DAW.
As for the “output” knob: That’s where you want to set the level, not the master in Cubase. You are dealing with two different issues here; the signal inside Cubase which you eventually will render to a file, and on the other hand the signal that gets sent to your speakers for monitoring. If you think your monitoring is too low but your internal signal is fine then adjust the output on the interface. That’s what that knob is there for. It doesn’t matter much if it means it’s at 12 o’clock, 2pm, 3pm or full up, unless it’s a noisy interface.
So, yet again: Import a professionally mastered commercial recording. Put it on a track. Leave track and master faders at zero/unity gain. Set your speakers at +4 to begin with. Set your UR22 mix to ‘full DAW’. Set your output fully down. Slowly turn up your UR22 output knob until it sounds loud enough with that commercial recording. Done.
If your mix at this point doesn’t sound as loud it’s because it’s not mastered and just mixed. To deal with this you have a reasonable option:
A: That commercial song you had was louder because it was mastered, whereas your mix isn’t (until you master it of course). So, lower the fader on that track until it’s as loud as your mix. Now everything will be soft again. Solo the commercial track with that fader still down, and go back and turn up your output on the UR22 again until it’s loud enough. At this point you’re able to mix to the point of it sounding nicely loud and pretty close to a mastered track, and you just have to remember that any commercial track you import and play back for reference needs to be lowered to match.