I wouldn't say a Firewarrior's armor would be AP 6 on the chest and head. Based off of the models and fluff and translated into DH, NOT the games (where balance is an issue), I would say the AP of the chest and head should be a max of 5, maybe even 4. The legs and arms should be one or two lower then, since you could argue they are similar to an advanced Mesh Armor.
FW Carapace should not get an armor value against a bolt weapon….
Something I would add on there would be a positive and negative modifier to hit based on time spent aiming, considering that the Tau's eyesight is not necessarily worse than a humans but takes longer to focus. So to simulate that, you could have any shot taken by a FW who has not used some sort of aim action to be done at a -10 penalty. Then to compensate for the fact of aiming and the Tau's advanced targeting systems and other things found in their helmet, increase the standard bonus of the typical aim action by 10 or something. Also, I would say, the Aim actions for them would take twice as long so simulate their eyes focusing.
As for the weapons, someone said it earlier. The shoddy WS, mediocre armor, and need to spend time aiming of the FW should be compensate PER FLUFF by their strong basic weaponry. Considering the fact that Tau Pulse weapons are essentially a downgraded version of Plasma, and using DH statlines, I would say 1d10+5 (bolt weapon) isn't too much. An AP of 1 though, is stupid. An AP of 3 or 4 would be sufficient. I would also change the range. A pulse rifle would in all likelihood be somewhere around the range of a hunting rifle, 150M or longer. Tau are supposed to be able to reach out and touch you from very far away and in all likelihood kill you. FW teams are supposed to be extremely deadly in that regard. This is compensated by the fact that, if you get into CC you will kill them (as feats of physical strength and hand to hand combat are vulgar to the Tau). Or at least into range with really good Imperium weaponry. Then take the chance they won't retreat to another spot to shoot the piss out of you from. The GM should NPC Tau like such. Engage at range beneficial to your forces, and retreat when casualties or combat advantage is lost to engage again when you have the advantage again.
Remember, even the might of the Damocles Gulf Crusade against the vastly outnumbered Tau Empire still ground to a halt. In part due to the strength of Tau weaponry, their philosophy of warfare, and their combat tactics.
Oh, and if anyone decides to put a rail rifle into DH, you might as well make its damage an instant KO if you hit….
I mean, it is a SP traveling at…. a minimum of probably Mach 3 or 4. That would rip most anything to pieces or knock a sufficient badass guy on his back, balance rules aside and actual physics taken into account.
