By old school death and thrash Im taking in these bands just for eg....say... Obituary/Death and Slayer/Sodom. Now they have compressed highs which make them a pain when listening through a harsh system ,in my opinion a laid back/warm system with a right mix of energy make them sound good. But then we all have budget and it is here where we have to start compromising.
Since you want a movie experience and want "COD" also its better to go in for a surround system,since you already have monitors. A good one would be the Onkyo HT-S 3500 for Rs 28000 max. But IMO if you can extend the budget better get a Marantz 1501 and Boston Soundware XS 5.1. 22+24 = Rs 46000.
Klipsch , JBL and some lower end Jamos have that PA effect when driven hard but they will cost quite a packet with matching amp. You have to hear TOOL's Schism/Jerk Off (live) on Klipsch and Denon (stereo)combo ..... hair raising scary......
Dont spend a dime on a soundcard because both Onkyo and Marantz have Digital ins so they will clock the incoming digital signal from your motherboard.Just buy a good digital cable.