Sounds like you are making things a bit difficult on yourself giving your instruments "inabilities". If I were you, and had ONLY one 5 string bass, and the standard tuning for my band was drop C (for example). I'd drop tune the B string to an A and tune the other four strings to (CGCF).
Most of the time you would use the "B" string as a thumb rest considering most metal utilizes a LOT of open strings. Since your guitar players probably use standard 6 strings, you would mostly be using the bottom 4 strings. When they go to "standard" tuning, all you have to do is tune your "E" string up a whole step (D). And you will never be lost. Not do you have to buy whacky string sets to make it "work".
Hope that doesn't sound too confusing...
Or maybe easier to sell your 5 and buy a 4 string? I only utilize my 5 string basses when my guitarist is using a 7 string. Otherwise I'm using a 4 string bass (tuned CGCF) ..like say..Killswitch Engage for example.
Power wise, I have to compete with two 150 watt amps! It's ridiculous. And the only thing that even remotely keeps up is the Ampeg SVT 4-Pro with an 8X10. While you don't NEED to have an amp with 10,000,000,000 watts, it's nice to have the head room when competing with guitar "ego" haha.
If you are still having trouble hearing yourself. Either convince them to turn down a bit (I know it's difficult playing this style of music!) OR not only use your bass amp, but go through the PA!! Mic it or go direct using an XLR cable. That will definitely help
But if you are serious about being a "metal" bass player. I HIGHLY suggest you save your $ and buy these things:
Spector Bass (A Euro or a Czech SSD if you can find one). Trust me, if you want to stop being frustrated with tone, these two are the way to go! (Ledgend and Spector core aren't as good imo). Save for a year, two years..I don't care what it takes. You will NOT be disappointed or frustrated with your bass tone ever again. Fantastic quality and ALMOST as good as a USA Spector for a fraction of the cost.
Another decent option is the Fernandes Tremor 4 Deluxe bass for this style of music. It's a bit cheaper (quality/sound wise) but probably a close second for METAL if I have to play anything else (it's honestly a toss up between this and my Music Man Stingray bass when I need a back up bass). I got a great deal on the Fernandes, so keep a look out.
Ampeg SVT 4 Pro and 8X10 cabinet
While this stuff is heavy and fairly expensive. You can find pretty good deals on Ebay for the head itself. Then find a cabinet that could utilize the power. There is no better head for METAL imo. But Mesa Boogie makes some great stuff and you could also find a GK that could also do the job.
Tech 21 Sansamp (rackmount or stomp box)
Beg, borrow or steal one of these (kidding on the stealing part lol). But you will LOVE this thing. It gives your bass some really cool overdrive without compensating tone. Check out the band KINGS X and listen to that bass tone. You can't go wrong with the Doug Pinnick tone. Bass players have tried to steal his THUNDER for years. It has a similar effect and may mask a "weaker" bass tone. (Suggested song would be "Dogman" to get an idea).
O.k. that's my two cents. But again, you will NEVER need another thing for that genre of music with those tools. My priority list would consist of cheapest to most expensive. The sansamp is a good place to start!!!