When I had my R1100RTL it had built-in speakers like the LT. After a year they sounded pretty bad. Never had much volume with distortion either.
I took it to a car stereo shop and they fitted some Polk speakers that were marine grade into the thing along with some sound foam or something behind them that improved the sound too. The old stock ones actually squeaked when they pushed into the middle of them. The middle portion of the speaker was the mid-range or treble, but it sure squeaked. New ones were more wattage and could be played at a higher level to hear them. Stock ones were pretty bad. BMW has never really had a decent audio system compared to other brands (i.e. Harley or Gold Wing).