The main problem is the guitard's tone then. Talk to the other guys in the band to see if they agree that his tone is poor and then have a chat with the dude. Guitards can be sensitive about their tone if they are a diehard gearhead (or stuck in 80s hairmetal glory days - played with a few of those), but often they can be rather understanding about these things. Sometimes they are just clueless about how to get a desired sound so they stick with whatever single setting they've come up with that they like.
About his songs - if 75% are yours, then grin and bear it as his are few. Again, talking to the others and see how they feel could be helpful - if they feel similar, try instituting a democratic policy for deciding which songs to do. If the guitard's songs get voted down consistantly enough, he may decide to leave the band (all problems solved and nobody got the boot). If you do continue to play some songs that are his, you can make the tone dispute easier and let him use his preferred shazz tone on his songs and change it for the other songs where it is less appropo.