BHP and torque are related and so by increasing one, you will increase the other. Power |EQU| torque * revs with a few correction factors added in. This is why peak power occurs at high revs and peak torque can occur lower down the rev range.
The way that I believe Ralliart get the high torque on their cars (like the RS450 and the ExtremeS) is to run with lots of boost in the midrange (approaching 2 bar in some cases) and then turn down the boost higher up the revs to protect from detonation.
What you need is a nice big spread of torque across the rev range as this will give you the 'kick in the back' performance.
The best way to achieve this is with the standard exhaust / induction mods and then get a programmable ECU or add-on controllers to be able to map the boost, fuelling and ignition to give you a big fat torque spread across the midrange revs while keeping safely away from detonation at the higher end.
Hope this helps and I'm sure other people will have other advice.
Is it strictly torque you are asking about or driveability? These are quite different things. It may be that rather than just increasing peak torque looking at how the power is delivered may be a better option. I've talked to a number of tuners about torque vs. driveability and Dragon Autosport had some good ideas, including fast spooling turbos. Might be worth contacting them.