I know it is an old thread. Propably everything has been said and done. I just want to mention that
- the 888 sounds great (also with the 888 OS on the 999), I mean REALLY GREAT
- tracks in one pattern have all the same length
- the 888 has other samples in the first 4 slots than the 999
- the sequencable stereo filter in the 999 is really complicated and better shut off
- the 888 has an extra parameter for base drum and tom for making pitch decay longer
- the metallic noise feature of the 888 vs the 999 is, well, nice but not more
- the mbase11 is the base drum of the 999
- the clap is not analog
- there are only 2 toms
- accent doesnât work on toms (bug)
- odd pattern lengths are only up to 15 (because A/B have the same length) (888/999)
- song mode works if you know how (differently on 999 and 888!)
- in performance mode selected drum kit is saved with the selected pattern
- the buttons are crap and need replacement after a few years no matter if used or not
- the backup-battery is soldered (!! )
- in the 09 samples have different tunings - so no mixed hihat and clap in one track in performance mode
- the snare has few sweet spots on the extremes (09, 888, 999)
- up/down is ONLY for patterns, not for navigating
- you have to save a pattern before changing it
- custom 8bit samples sound GREAT
- there is only a filter for the HH-sample, not for the other sample tracks in the 888/999
- the VCA for the samples is ⌠strange but usable
- shuffle is possible on all xbases, cumbersome on the 09 AFAIR, set per track in each pattern in the 888/999 - sounds great but is a lot of work
- the computer sample transfer programs (yes, plural - one for 888 and one for 999) work fine up to Mojave (!)
- the 888/999 needs to be reset manually to internal clock after EACH whatever-data-dump to the machines
- there is a traditional accent track on the 09 but not on 888/999 - here you can add accent to every already set step by double clicking the instrument button
- in order to live tweak the parameters of each instrument you have to select the instrument by tapping pattern write, select instrument, then come back to main
- the midi tracks for sequencing external equipment from the 888/999 are ok but not more - no programming of velocity
- you most certainly need a mixing desk or submixer in order to EQ the snare (esp. on the 09), set CH/OH balance on the 888/999, give the delay to the HH and the reverb to the clap and for every filter trick - you will need an external filter or modular or semimodular synth for that, too
So basically the 888/999 is like your borderline girlfriend/boyfriend - energetic, fun, forceful, great in bed, experimental, connected, smart - but you have to be mindful ALL THE TIME else REALLY BAD THINGS can happen. These machines are like russion photo cameras. Follow the routines in the handbook exactly as described - donât do anything else, you might break it.
The 09 is plain and forward. Too bad there is just one sample track and the built in samples are not tuned to the same tuning (I guess he used the original raw samples - they have to be played at different clock speeds I think - at least thatâs the case in the 626 and 707 AFAIR).
Since things have been the same over decades with Jomox (seems to be more interested in producing new and really complex stuff like sunsyn or a neuronal synth instead bug fixing) I suppose it wonât be much different with the alpha base. Will have that Jomox sound. Has a more complex membrane track. Built in sampling capability (HiFi ??? !!), built in FM-track, NO song mode anymore. That said you are propably better off with a 888/999 and a modle:samples and a model:cycles⌠(still cheaper than the alpha base).
Apropos: the 888s are considerably cheaper on the secon hand market than the 999 - although they have the better sound engine (additional parameters) and so far I found nobody who could make good use of that strange filter in the 999.
Well, maybe buying a rytm and a used mbase11 as side-kick 
or for sampling is the better option. Youâll have a much better sequencer and the most essential FX in a very useful package.
SCNR - but now I can forget about all that. It is written down