I can't do the actual comparison for you Squeak because I have very little playing time on a 550, but as you know I had the 740 and replaced it with the 2000. ( I also had a 530 before that. ) While my 2000 was away for repair I had a loaner 1000 for a few weeks. A lot of the sounds were similar on the 740, 2000, and 1000. There were noticable improvements on the guitar sounds of the 2000 / 1000 over the 740, but by and large the majority of sounds were pretty close when played through a similar sound system. The 2000 / 1000 had better sounding speakers. The 2000 shined over the 740 in the features area. Much better sequencer, better effects and control over them, and basic sound editing capabilities ( there were none on the 2000 ). The three boards' capabilities, when hooked up to my sound system and my computer ( using XG works ) were similar, but the huge advantage was that I could do nearly all of the same editing away from the computer with the 1000 / 2000. With the 740 I had to be hooked into XG works. I also thionk the harmonizer was a lot better on the 2000 than the 740.

It doesn't quite answer your question, but if we wanted to say that the 550 is close in quality to a 740, ( and a big improvement over the 530 ) then I would also say that the 2000 / 1000 are an improvement over the 740 / 550.