In short, Yes.
Longer version (without being too long winded about it): EQs are a perfect edition to a car computer setup, in my opinion. It allows on-the-fly tuning without having to mess with a small computer screen. The nice part of EQs is that most decent ones have built in line drivers, which is especially good given that the signal is weak coming from the built in sound card on your computer. I would say that a good portion of members that are using EQs have stepped up to using one with an optical or spdif input to it because of the benifits like surround or DTS and preservation of sound quality. I personally have become somewhat of an unoffical advocate of alpine's PXA-H701 Digital processor/EQ with the standalone controller rux-c701 because of the amount of functions and features so I would definitely reccomend that if you are willing to shell out the cash.