Tell your bass player to get out of your midrange region. You are also probably accentuating your lows in his area as well.
My bassist has a graphic EQ built into his amp. The frequency to choose from are 40, 100, 250, 625, 1.6K, 4K, and 10K.
The Dual Rectifier seems to have a resonance peak roughly around 172Hz - 205Hz depending on tuning (My experience here is all tone knobs flat 12:00, Guitars tuned between C and F standard tuning using half step intervals. C, C#, D, D#, E, F using A=440Hz).
Looking at my bassist's eq the closest slider to MY amp's resonance peak is the 250Hz slider. So, we pulled that slider all the way down, or out. Next, ALL bass guitars have a resonance peak at 800Hz give or take a few Hz. Seeing that 625 on his EQ is still slightly in the guitar's spectrum, we pulled that slider back about 3Db, but increased his 1.6K slider to shift the peak between 625 and 1.6K as close to 800Hz as possible without using an outboard parametric or another graphic. The increase was not quite 3Db and we had to slide both frequency sliders back and forth at same time until the 800Hz would pop out(very noticeable frequency for bass). Gave him a little boost at 4K for pick click (he plays with a pick due to nephropathy in his hands due to cancer treatments) and killed high end hiss by rolling back the 10K slider about 8Db. Mind you this was also with his treble and bass eq knobs at 12:00. The 40Hz was boosted until you could feel something low frequency change and I increased the slider gain. The 100Hz was increased until his lows became solid and not mushy.
Now we played against each other. Both guitars and Bass. Now the guitars had come forward, but now bass started getting lost. Now I had our drummer increase the bass knob EQ until there was a distinct different low frequency heard by all. Increased it until it became slightly overpowering, then backed it off until right before that point. Next the drummer increased the treble eq knob until the bass popped right out and sounded perfect.
It actually sounded like a cross between DD from Overkill's bass tone on Elimination and Steve 'Arris' overall tone until he hit the on switch to his Shitbox(dude loves Cronos' bulldozer bass sound but wont accept Cronos' tone comes from him playing through a Marshall Superbass cranked and he kills his tone with a Boss HM2 not set to Swedish deathmetal settings). even when his amp will distort using the tube channel :twisted: :evil:
Find the tone you like first in a band setting. Especially when playing metal. The bass should compliment the guitas tonally while retaining a character of its own. the only bands that I see doing that different are Iron Maiden and Motorhead. Meshuggah actually tunes the bass higher than the guitars and attacks the tone spectrum from that angle, but that is because the guitars are tuned so fucking low the bass is used to clarify their muddy tone. Saying this the guitars have to compliment the whole package. Have someone the bad knows and trusts and who has a good ear come in and listen to a rehearsal and give you guys an honest opinion on guitar/bass tone. Then make the changes to see if an improvement is made. Dont have an ego if your tone sucks and you have to change. Guitars in a band sound different than guitars at home. Once you get the band settings down on YOUR tone use the same sound at home so you can avoid the whole I love the Line6 Ultimate setting cause its badass scooped **** newb mistake. Once you get used to band setting guitar tone at home, you will learn that most tones more inexperienced guitarists choose sound totall garbage (one of the main reasons why I wear ear plug into a store like Sam Ash or GC), and it will make you want to go change a dude's settings on the amp he is using or go drop kick him in the chest(depending on his skill level). I am being faceteous here, but this is the reason why experienced guitarists(or those old farts) complain about a younger dude's tone.
Short example then Ill shutup. Randy Rhoads tone. Fucking Epitome of Heavy Metal guitar tone period end of story (**** you it is not hissy go **** yourself old man you dont know ****, go listen to Led Zeppelin or some other old fucker music). The words insde ( & ) are MY personal beliefs to this day. No his tone is not hissy, but compared to the guitar tone of UFO, Ted Nugent, Kiss, Black Sabbath, Scorpions, Judas Priest, Tigers of Pantang, Queen, etc.. from THAT era of harder music, yes it was hissy. BUT not due to his Altec Speakers loaded in his cabinets. It was because he was using a MXR Distortion+ followed by a MXR 10 band graphic pulling out all the garbage frequencies of that pedal while simultaneously tailoring his EQ to be as harsh and offensively aggressive they could get his tone to be to launch Blizzard of Oz's as the hardest, heaviest band at the time. Which it was, until a Accept released Restless and Wild which essentially anally raped Blizzard of Oz then went *** to mouth without washing up first with the opening track. Guitar tone peaked with Restless and Wild across the metal genre for crunch and tone until Scott Ian upped the bar with Stormtroopers of Death's guitar tone(one he should just go back to using and stop with trying to chase that dragon). It changed again with Swedish death metal, then eventually went back to approximations of S.O.D. mixed with Possessed, and Bolt Thrower if those three band's guitar tones had a threesome and modern guitar tone is their offspring. Nowadays the only guitar tone that sounds somewhat different than others is Vader, and all they are doing is approximating mid to late era thrash/death metal via eastern European technology. Piotr and Spider use Piotr's two channel Dual rec to record with and Dual Rectifiers live. (Now Laboga Mr Hector, but thats a DR clone). Me? I try for the black sheep of the family if Restless and Wild, Seven Churches, and Speak English Or Die guitar tones were Human Centipeded in reverse and shat out a guitar tone. Do I sound like that with my tone through my DR? No clue how close I am, but those three albums tones are the overall I am gunning for (maybe my wishing makes me feel good about it and thats cool too).
To recap, You and your bassist are walking over each others tonal ranges. Carve out holes for each other. Create a band tone, and stop using a **** scooped tone unless it augments ya'lls music(Deicide's worked for them but their guitar tone?, man!). HAVE FUN!!!