My old Parasound pre-amp has tone controls on it (center freq is at 100 hz and 1Khz). It also has a bypass switch, which I always have enabled.
My music server is running JRiver Media Center and Jriver has built-in tone controls as an option on the DSP.
At this point, I'll never need a pre-amp with tone controls on it. I run JRiver flat (with the EQ DSP capability turned off). I have played around with the JRiver DSP Eq and it has no imaging or soundstage impact that I can tell.
I haven't look at the JRiver plug-in capability, but it looks like there are a lot of options there.
HsvHeelFan