"crappy speaker" = satured and distorted engine notes if make you feel better.
So you are claiming that all Forza sounds are saturated and distorted are you?
Not only is that rather incorrect, but it's still flamebait.
That is one of the general changes that people demand in GT5 sound. More punch.
With good reason, GT5's sound still requires quite a degree of work to accurately recreate how the human ear hears an engine. No game has nailed it 100% yet, but currently GT5 is one of the furthest from it.
GT5 audiophile sound: High frequency rate and detail (clarity), 7.1 uncompressed output, full dynamic range and detailed multichannel sound position.
So just LCPM then (because that's what LPCM gives you), none of which makes a blind bit of difference if the source sounds were not recorded well and/or poorly mixed and/or poorly produced.
GT5's samples could have been recorded 100% faithfully yet if they have not been mixed and produced to meet the end needs then no amount of 'audiophile sound' is going to resolve the production issues.
All recorded and reproduced sound needs to be mixed and produced to ensure that when you listen to the recording it matched what you would hear 'in the flesh', and that is primarily what GT5 is missing.
LPCM gives you many advantages, but if the source doesn't do it justice then its pointless using it. A well mixed and produced DD/DTS track will still beat out a poorly mixed and produced LPCM track (a point illustrated by the first release of Black Hawk Down which had a shockingly poor LPCM mix that sounds far poorer than the original DD mix).
The quality of the samples does not change but how they sound all togheter and mixed in one, two or seven speakers makes the difference along with the enhancement or equalizer presets that you use in between. Clearly seen in the sound detail between the two Gallardo vids.
More speakers will simply give you a better placement of the sound, its not required for dynamic balance at all. My hi-fi (2 channel) offers a better dynamic range than my AV system (as it should given the price difference), however both still require a quality source to be able to shine.
GT5 does sound placement very, very well and in that regard to audio is well balanced, however the mix and production on the raw audio still leaves a lot to be desired for the majority of cars.
"In a more large scale" = Means more range to play with the sound frequencies (or boost some sound layers) without peaking them and sounding bad. Not that you can edit the sound only in GT5.
All of which still requires a well mixed and produced audio track to begin with, if you don't have that then a greater dynamic range will not provide you with a great advantage at all.
Through my system I get zero harmonic distortion from either Forza or GT5 at well past comfortable listening volumes, and yes GT5 does sound better through it than straight to TV speakers, but so does every other racing sim.