gt 940m pair with i5 is not that bad. If you don't mind lowering the resolution and some details, you can play most new games in low to mid settings. The hdd size 128gb is a bit small though.
https://www.youtube.com/watch?v=u2l3S99nZII
It will run decently with not so demanding games like gta V
https://www.youtube.com/watch?v=AXXbZF822RU
but will perform poorly in demanding games like witcher 3
https://www.youtube.com/watch?v=oKZg_f8h3NQ
The gpu is 850m and cpu could be i5 or i7. This video show 850m in action to give idea how it will fair with a demanding game
https://www.youtube.com/watch?v=6RzlCAwU3sg
Go to msconfig then under startup tab disable all. Under processes tab, click the box to hide windows files then disable all. Restart then let me know if that fix the issue
as long as the power amplifier has a subwoofer out, you can plug it in. The question is how much the sub out max watts is allowing you... look at the wattage for just the sub out. It usually tells you max watts it can power up