Before I started using a LMIII, I used a PA amp (1000W Carvin) and a parametric equaliser, on the grounds that I wanted a clear, clean sound that I could eq to my taste. I didn't want any distortion, valve "warmth" or flavour-of-the-month "tone". When I plugged the Markbass in, I found that it sounded similar to my PA amp setup. Clear, clean, flat. I didn't do any in-depth comparisons, but I am fairly confident that the Markbass did not colour the sound of my bass.
I can't suggest any brands, but I think that's what you're looking for.