Interesting, when trying jazzes out, I found the bridge pickup sounded nasty through a Markbass combo, the shop swapped me to a Rumble on 'vintage' setting and joy was assured.
It's interesting that people think a 'speaker without tweeter' amp won't fizz, I found most combos with a dirty channel (e.g. Orange Crush 50) sound pretty fizzy. I do like the way the standard channel on the crush amps sounds when they are pushed though.