My system is a little on the dark side and I've used many tube phono stages and now I'm finding that a solid state phono stage is really better for me. Helps the overall balance.
A classic example of applying a band-aid instead of addressing the problem at its source. That's not the path to high fidelity IME, certainly not at the performance level this thread is about.
If a system is a little on the dark side don't paper over the problem, identify which components make it dark and correct or replace them. It's impossible to counterbalance the distortions of one component by introducing distortions in another. In a sufficiently revealing system all you'll hear are the competing distortions.
Make each component as neutral as possible. That's what the best preamps or the best anything seek to do.
Harrumph! ;)