Here goes:-
MP3's will never sound as good as the actual instrument itself. Everyone has different tastes, different ears, different setups when playing them back etc. so what may seem harsh to some will sound wonderful to others. Some of the Tyros demos do sound good (guitars), some sound very tinny and weak to my ears, it's a case of you have to be in front of the keyboard in question.
Answering the questions below:-
1. The speakers are built into the keyboard and are excellent quality. Gem will be releasing a case for it soon, but I've telephoned lots of case companies in the UK and all could make one for a Genesys. The stand is very good quality and does not sit about 3 feet above the keyboard, it is perfectly placed. Some Technics have stands mounted higher.
2. The Genesys's sequencer is 32 track and is very easy to use. Being an SD1 owner too, I find the Genesys far easier to get to grips with.
3. Midi file playback all depends on the company/source of song you are using. Genesys is certainly on par with any Roland I've heard (I use a G1000 and also had a VA76 for a few weeks before deciding it was not very good for a live performer). Gems own songs are excellent and so are my mates company which is www.songgalaxy.com
He offers midi files and MP3 format songs and all have demos to listen too before buying, check it out.
4. The Genesys is nothing like a SD1. I was worried that it may be at first since Ketron have made the speakers/amplification I think for the Genesys. Also, the Ketron SG1 is a Genesys under a different name, very confusing. Genesys sounds are totaly different to SD1.
Since the Tyros doesn't have a hard drive, MP3 playback, CDRW etc. I'd say the Genesys is far more versatile - listen to both and judge for yourself.