I had an mpc 60, 500 and 2000xl. The 60 is just a stripped down 950 without the editing options. So if ur after that mpc60 sound just get a 950. The 500 was nice for on the go and to take out to a friends studio with ease. Sound quality was meh imho. The 2000xl I had for about a year and then I switched up to an mv8800 witch I still use today. I absolutely love this machine. It's a big ass dedicated computer made for sampling. The sound quality is very honest. Whatever you put in it you will get out of it.
I also had an s5000 but I thought that sounded weak and the interface was a **** to get around with.