first of all make one thread for ur queries. its confusing to go through 2 threads for the same problem.
secondly when it comes to the little details that will make the difference between you being able to listen to good music, these kinda amps will make sure u dont get any. ofcourse you cant distinguish between the music u listen to unless you compare the chinese amp with a branded one.
(look through the electronic sales section, there are quite alot of 4-channel branded amps on sale. u can also contact madhouse12 or kriger since the two of them always have some amps with them)
finally, u can get a 2-channel amp for a sub but again, not the chinese ones. u also need either a S4 or a D2 spec subwoofer, since a D4 will be running at 8ohms on bridged, and at that impedence, ur amp will be sweating alot. an S4/D2 sub will run at 4ohms on bridged, and the amp gives the most rms on bridged at that load.