When you say tune it, what re you thinking about ???
The amp gain should match our head unit output level or the previous piece in the signal chain (ie x-over, EQ, etc). It's not a volume control.
If it has on-board X-over, depends on your setup configuration........ components on a passive x-over (2-ways or 3-ways), subwoofers, etc, etc.
Bass-boost circuit............ depends on how heavy you like your thump.
Honestly, you CAN do it yourself. Post what you got and I'll try and talk you through it.
Current : 2013 Mini Countryman JCW
Past: '88 E30 M3, '69 BMW 2002 Ti, 2000 328i, Audi A6 TT, BMW X5 3.0i , Audi A4, Mini Cooper Clubman S 1.8T