the ASR-X sucks major when it comes to the sequencer, i have owned one, and i can honestly say the RS7000 and MPC have better timing. the ASR-X's clock is very instable and is really bad for making good sequences, the effecs are nice, but very much parameters to change (that can also be a pré !) the samples are clean and good. i actually never recomment anyone to buy these things, aspecially because ensonique is no longer giving any support and because of the bad timing of the processor !!!

The MPC i know very little about ! so that's for u guys to give opinions !!!

The RS7000 has a good sequencer with very good timing !!!
easy OS updating is possible just by using flashmedia cards so you don't have to open your machine to update the software inside ( don't know if the pro version of the ASR-X has this but the non-pro version has chip updated so you must open the machine and insert a new chip in the machine ! )

The sounds are clean and very good, the effects are very usefull and you'll only be able to change some of the parameters but enough to change the effects to get your sound you like !
only thing i do not like is the fact you have a patternchain mode between the pattern mode and the song mode, but there must be a reason for that i also would like to see much more scene memories on the machinem because i use them alot !!!