VS880EX vs. VS840EX

[jelly]

In fact, I really interesting in 880EX. Including its built-in f/x , Automation , SCSI port , time compression , balanced inputs. But according to its price which double from 840EX make me have to think carefully.. About the alternative , the 840EX. From the above feature of 880EX , is there anyway can I do it in 840EX? Such as automation , I heard that you can record automation with 840EX if you have sequencer (i have Cakewalk). BUt how can I connect 840EX with computer? via midi cable or via scsi port? for scsi port 840EX will need to buy optional card right?
About time compression , does it useful? Do I really need it? And does 840EX allow me to change pitch?
The last one , balanced inputs , is it much diffirent to 840EX's? 880Ex's is TRS , is it can connect with XLR type preamp? I don't know is it much audible diffirent?
Sorry for a very long question but I really appriciate if you answer me.. I really need the info..