They're two very different synths. I own a JD800 myself, and although it's interface may seem close to VA, it definately is not. It offers a wide variety of samples which can be processed trough 3 envelopes (1 for pitch, filter and amp) and 2 LFOs per layer, and up to 4 layers can be stacked for one sound. It offers a huge amount of programming options and is very hands-on, and thus will enable you to end up with very interesting sounds, specially a wide variety of pads, but also leads and basses.
As far as I know about the JX10, this is 'just' a digitally controlled analog synth, though with 4 oscs per voice, as well as cross modulation (amongst others) this may offer some very usefull analog sounds. As far as I know filters are not resonant. Programming is done by selecting the parameter and changing value with a data slider. This may be quite tedious. At least, it's not usefull when playing live. It's sound is said to be very suitable for disco/italo/synthpop, but should certainly be able to do some very good warm analog pads too.
Taking you use it for film/soundtrack purposes, I'd definately go with a JD.
Hope that helps
