Are you sure you need an all in one box? You've tried a few of what I might originally suggest, MPC, ESX and if you added a microkorg or synth with bigger keys if you wanted, you'd have a fairly portable system. In fact, I think the ESX is a great live tool, if they'd added some poly ability it would be even better for those that like chords.
ESQ-1 or SQ-80 are original workstations with seq, multitimbral and proper programable 3osc architecture. Adamski originally played live with one and a 909. One issue is no internal fx and theres only L/R output. It also sounds like you're maybe looking for something newer , usb, computer backup etc + more portable.
I tried the minikorg workstation in rubadub and its got nice quality sounds, i didnt investigate the workflow though.
I guess it depends on what you're presenting live, if you want full seq control, switching patterns, muting, playing a live track, sampled sounds or programmed synth stuff or happy with rom-type presets. mini keys or fullsize?
other options -
DX200/ monomachine/ posh groovebox and use a controller keyboard
mc303/rm1x/shit groovebox - hey, don't mock it, ur used 2 x mc303 live
w-30, EPS16, ASR sampler workstation - but you've already tried ASR, plus these are heavy things
nord modular - preprogrammed with seq's and prepared stuff
korg microsampler?
or the most portable of all, gameboy & palm with bhaiji's loops and microbe