need help with Rom flashing

hello all.
all the info out there is really confuse me.
some one please give me a valid links to here.

please correct me if im wrong somewhere in my understanding:
i own xperia Z2. my version is 5.1.1 stock.
the sound is crazy low ( after i put the max db at setting-sound...), so i searched what can i do about it, i've found there is a mod that fix this. as i understand, for that mod i should have recovery and rooted device, so i thought to myself "hey, if im gonna do root and install a recovery ill also will flash a nice rom"...
so i tried to follow some guides here but they are realy confused me.
at the links it says the root won't work for any device...
also it says it is gonna work for lockboot or something...
more over there is many methods and i dont know what is the simplest one.

there is more info that realy confused me and i want to be 100% sure im doing the correct steps...

I know i need to root and install a recovery, then i i need to pick some rom and flash it ( right?)
so please give me a links to here for what i need to flash a rom for my sony xperia z2 device ( v 5.1.1 stock).

ty for helping.