It depends on the preamp, and what type of tone controls the preamp is replacing. Probably 90% of aftermarket preamps have a particular "sound" when set flat. If a player likes that sound, then yes, he/she will probably keep the preamp set flat.
My tone settings are kinda similar to yours, only I have certain frequencies boosted on my amp (Eden WT800C). When I say boosted, I really mean just a slight bump in a given frequency...maybe 3 o'clock on the dial at the most. I also will regularly boost my hi and lo mids all the way, with the bass and treble boosted maybe 70%; gives it a really thick and aggressive fingerstyle tone. I have a Pope pre in my Cirrus, and it has a 4-band eq, so it was a tough time not making redundant adjustments between the bass and amp. I'm not one of those "transparency" guys, I'll boost a control all the way up if it sounds good lol. That said, I'm still trying to find the right balance...sometimes I feel like I have too many tone controls that are set a too many different frequencies
How is your DI setup? Is it pre- or post amp eq? I would think that would affect the sound through the IEM's and wedges greatly. It it's pre eq, then adjusting the controls on the amp aren't going to affect the sound coming from the board. Conversely, if it's post-eq, the opposite applies.