huh, i have used plenty of clients on sify.
To use any client all you need to do is change default port from 6881 to something else, thats it.
I am using azureus as well as µTorrent. Both work well under sify's NAT.
I use azureus for torrents with dead tracker, used to be bitcomet user but stopped using after the problems with leeching and specially with amount of data it used to drop.