Having both I can say the Motif is not an Arranger by any stretch as in oder to make it "arranger like" you have to create everything by stringing together different ARPS yourself poking and hoping, experimenting which takes a lot of time all of which is done for you already on the Tyros.
This is easier to do in some cases because of the pattern looping mode. But not by much. In many cases I like to use the Tyros arrangements and port the MIDI information to the Motif sound set as a start and go from there. Since I am in most need of Bass playing skills and cannot create the guitar parts in real time I used to play rhythms for the bars I needed switch the chords and record another few bars and string the results together because I cannot change chording smoothly in one pass. The Motif and Tyros has been a boon for me in that regard. I would buy as many Guitar ARPS as would be available.
ON the Motif many sonic details can be edited in real time. The effects routing is pretty complex as complete as well. I have had it over a over a year and I still have not touched 50% of the features. Very intimidating ubtil you approach it from the standpoint of learn what you need when you need it.
I think they compliment each other but one would never replace the other on many levels. IF one loves programming and wants to create original arrangements that cannot be found in the arranger world, the Motif would be the better choice after a long learning curve. You have to PLAY everything on the Motif. Most of the Tyros plays itself. For cover tunes the Tyros is much easier to get results from. For live play one had better have an IATSE stagehand nearby to load and unload the thing or personal roadie.
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Yamaha Tyros 4
Yamaha Motif XS8
Roland RD700
Casio PX-330
Martin DC Aura
Breedlove ATlas Solo
Bose MOD II PA