Soundchecking is an art, and if you let anybody from the band do it - with the possible exception of the bass player! - they will mostly pay attention to their own sound, and turn down anything that appears to interfere with that.
While I'm in no way a pro, I have a certain amount of experience in making a band sound decent at The Dog And Duck. First of all, the acoustics of the room can fool you, especially for the low frequencies: they are prone to sound really loud in certain places and really weedy in others, and I mean 'places' in the same room. So walking around while listening is a must. What you were hearing, @stewblack, may have sounded a lot better a couple of metres to the left or the right, for instance. And of course when the audience was in.
Another important thing I've learnt is that having a majestic sound in the rehearsal room, or in your own practice room, away from the band, means very little. I have lost count of the times @Happy Jack and I have had to make changes to his pedal settings, or EQ, or both, just because he would otherwise disappear in the mix, or indeed overwhelm it, as the case might be. Precision basses are infamous for sounding great (if you like that kind of sound) while playing on your own or with the band at low volume, but ending up as a horrible muddy mess as soon as you start playing in the corner of The Dog And Duck by the door to the gents'.
So, er, you'd probably have to persuade one of the band's significant others to become your sound engineer. Short of that, boost the mids and cut the lows on your bass sound, counterintuitive as it may seem. At least you'll cut through and people might even hear you...