Drilling would depend on the quality of cable used. I used hifi stuff, van den hul and qed so holes had to be made for wiring to exit.
With hifi, how can a HU give proper amplification for speakers. If you see the size of a proper amp rated at say 60w per channel, none of the PMPO stuff, youd never think that you HU amp can match it.
Your HU may provide a great sound but this will be limited by cabling, amplification and speakers. No good scrimping on any of these. Amp would make speakers sing. Good quality cables would too.