I agree with eviljohn2. Behringer do graphic equalizers that should be able to do this job well.
The unit would be a 19" rackmount in format, but would lay flat on almost any hifi rack shelf.
Black & Silver, look quite nice.
The product below takes 6.3mm Jacks which would be the best option, as the others take XLR connectors which wouldn't normally be suitable for Hifi
31-Band equaliser should give you enough control I hope.
I must warn you that these items take 6.3mm Large Male jack plugs, rather than phonos.
I have a behringer rackmount mixer and rather than buying whole new cables, I would suggest get yourself some Phono-to-6.3mm Jack adaptors from Cableuniverse.
Cable Universe service has always been exceptional for me.
You will need 4 of these connectors, 2 to add onto your phono cables going into the unit and 2 going out. Nice solution as I use these myself.
Hope this helps.
P.S: It's the Behringer DEQ1024 you would need (confirm for yourself), but there are other equalisers that they nake that look exactly the same, but take XLR connectors instead, so watch out to make sure you don't buy the wrong one!