Regarding the Heartbreaker vs the Stilleto, have you tried having your other guitarist turn his mids down while you turn yours up? While a lesser ammount of mids may sound fine playing solo, it's easier to get lost in a mix with less mids, as mids are where a guitar cuts through the mix. Of course, depending on the roles each of you is playing (him lead, you rhythms) him cutting through Stiletto with the Heartbreaker may not be a bad thing. If he's still cutting through your sound with his mids down and yours up, you might try an EQ in front of the amp or in the FX loop to bring the mids up even more and give the sound the punch needed to cut through the mix.