Hello and welcome Nitin pande,
If you want to try bi-amping, use the NAD power amp for the woofer section of the Infinity Alpha 50s. The woofers always demand much more power than midrange drivers or tweeters.
True bi-amping actually involves using an external electronic crossover where you set individual crossover frequencies for each set of drivers, the slopes and the relative levels, bypassing the Infinity internal crossover entirely. It has real benefits for huge outdoor concerts and big arenas, but the quasi bi-amping you proprose is unlikely to produce any audible benefits in typical domestic-size rooms.
Regards,
