I love to run pre amps hot, but generally nowhere near 20dB over 0VU.
It's possible you are damaging your signal by attenuating it post pre. Doing lots of gain adjustments in the analogue domain will degrade a signal. For a good clean signal (even if it is a distorted sound) 'Unity gain' should be the thing to shoot for.
What that means is that you gain the signal you want to record
once, and every other part of the electronic chain simply passes that signal straight through without introducing any imperfections (namely unwanted distortion or noise) by amplifying or attenuating that signal again.
Does that make sense?
The generally accepted (and AES) standard of 0VU = -18dBFS seems to work pretty well for most recorded music.
If you were to record a sine wave or oboe or any other fairly steady state signal that sits at around 0VU it will go to your DAW sitting around -18, which is a very useable level in 24bit digi land.
The thing that throws many people is that the VU measurement was designed as an "average" level that will not react to fast transients. Unlike your DAW meters that are almost certainly peak meters that read every transient.
So if you put a heavy Kick drum into your pre it may well read 0VU on your analogue gear, because that is it's average energy level and the VU meters will miss the transients, but when you look at your DAW that sucker is hitting -6dBFS.
What that actually means is you are hitting your pre amp way above (+12dB or more) it's optimum operating level.
Thankfully most good pres sound great when you start spanking them. Most decent new analogue gear has 20dB (the really good **** may have 24dB) or so of headroom.
You will start to slightly round off the transients and hopefully bring in some very pleasant sounding harmonics and distortion.
I hope my little rant makes at least some sense.
Short version would probably read: Calibrate 1kHz tone from gear at 0VU to DAW to read -18dbFS. Aim for -6dBFS peaks on transient signals.