f# tuning

Hello, i've been thinking of this for a while now and i'm scared to try it so i'm asking it here first. I've auditioned for a metal band that is pretty heavy. They use 8-string guitars tuned in F#. The problem is that i don't have any way to reach the F#. If i'd downtune, my strings will be...

So I decided to tune my 5 string Ibanez Mikro 2 semi tones up to F#1 to D3, from previous using standard E tuning, E1 to C3, since with the way I use it, I guess more sort of like you would use a Bass VI type instrument or a baritone guitar, playing a lot of simple chords and harmonizing, often...