The 840 series is discontinued. I have the 840EX version and its a good machine though it's not a true 8 track. tracks 5/6 and 7/8 are stereo pairs. I believe that the 880 EX is discontinued as well and the 890 is on its way out as far as i know. As far as the recording 8 tracks at a time with 6 inputs on the 880, I have no idea. You may want to compare hard drive sizes on the 880 & 890 vs other recorders in that price range (new or used) because i think they are fairly small compared to what is out there today. You may want to check into a used 1680 or 1880 as the prices are comparable to a new 890 (i think).
If your scouting for a good recorder check out some of the new Akai stuff.
The new roland 1824cd looks pretty kick ass and i hear good things about the boss 1180cd. Of course that is all subject to your budget.
Good Luck!!