DENON and MARANTZ has dealers in karachi, they will ship your receivers to ur door step, same is the case with yamaha i think, im not a fan of onkyo, so i wud personally opt for yamaha RXV series or denon amps, alteast supporting dolby true HD or DTS HD. these cost 600$ upwards, and usually available in Pakistan with a little with premium over retail prices.
u can mix speakers, but its better to have voice matched speakers, specially front three speakers.
PSB speakers, Klipsch, B&W, Jamo, Bose, are also available in Pakistan thru authorized dealers. prices of B&W dealer were outrageous, PSB on the other hand had reasonable prices compared to internet prices.