The sound (speaker) answer is always going to be user/personal opinion. In my opinion:
EVO 4G
Speaker during calls quality: Okay, not great. Seemed to crackle on bassier or lower sounds but audio quality in general was kind of flat
EVO LTE
Speaker during calls quality: The bass and overall EQ of the calls seems a little better then flat. No buzzyness with low-end sounds etc. Well rounded and acceptable for calls producing good quality reproduction
EVO 4G
MP3s, locally loaded songs playing: Decent output, well adjusted EQ. Reminds me of a BOSE system (no highs no lows, must be BOSE). With DSP added, much better quality so stock it needed help with overall quality, with DSP, perfectly acceptable for a cell phone but not as a MP3 type personal player. Then again, my Ipod Touch doesn't sound any if better then either cell phone.
EVO LTE:
MP3s, locally loaded songs playing: The overall output could be better, its not so low that is not acceptable to me just could be higher stock. Sound quality, EQ, in my opinion blows the doors off my original EVO and Ipod touch for comparison. With Beats Audio, to me it compares to DSP x 1000, as a musician (for hobby now) I love it. But again, its like a pre EQ thing, fixed sonic differences with overall mix, highs, lows, midrange etc. I hear much better quality just a tad lower in overall volume output.
Both seemed comparable with BT streaming of Pandora, XM, You tube etc running without DSP or Beats Audio. With Beats, again in my opinion blows the doors off the original.
Not a huge comparison but someone asked for more details in sound quality between the two and again, just my opinion.
The Beats Audio or tweaking the audio on the new EVO LTE produces some amazing quality. I have not personally compared to GS3 which is what this 'should' be about anyway but wanted to throw that out there.
I have recorded some good quality live music, guitar recordings etc and pretty happy with the results. Personally, for me..I love the sound and possibilities of this new EVO. I am rooted btw, running Fresh 1.0 for link updates and quick settings. I am using Nova launcher and have been since pretty much after I got the phone in late May. And using stock kernel. I do recommend a nice quality SD card with class 10 for recording and video etc, for me it made a difference (small) on playback quality compared to using the internal memory.
Hope that helps.