radio problems

[trs1975]

does anyone know why i lose bass and is not loud when turned up all the way. if i turn down the volume fast the bass kicks in and goes loud for a second. i did install new speakers in the front because the ones that came with the suv were shot. i have a 2008 equinox team canada edition, please help and if cant be fixed what would i lose if i install an after market radio.
thanks
tom