I believe the MEGA voices are multi Element voices that can be recreated to a great extent on the XS using velocity switching. IF one enjoys that sort of thing. To my knowledge that cannot be done on the Tyros. There doesn't seem to be a [provision for creating voices from 8 elements of ROM voices (like piano damper off which is an actually wave form that can be used as an element an edited in any way)

Only the SYNTH voice from the Motif were passed on the the T4 to my recollection. The Tyros is the FIRST instrument in Yamaha's digital instrument unit to get NEW technology.

I am sure they share a lot of voices, In fact having both I know they do however, the editing on the Motif is far deeper per element. I don;t see where I can select envelopes, effects routing, filtering, EQ on 8 elements of a voice on the Tyros. Most of that is done already. I have not done this but O believe you can edit the Multi voices on the XS using SW as well.The Tyros 4 is likely to cost more than the Motif XF XF8 Go figure.

@Leeboy I meant $1500 more than a used T3. That is the question T3 owners must resolve IF the T4 MAPS for $3999 and sells for $3500 at under MAP discount houses.
Im still waiting for my dealer to get an official price list so I can see what I can buy the T4 for at 10% below that and sell the T3 for a price a 910 buyer would think seriously about. I am looking for a $500 spread. Since I am not Upgrading the Motif I may sell the T3 for less and pay up t the T4,

The XF does not have what my XSF has stock. I don;t use the sampling feature Tyros and PC covers that well enough so the flash cards mean nothing. I do use the MLan FW which is an option now on the XF. Besides that Yamaha has said they will update the XS8 with the SW capability of the XF, More ROM is nice but having both the Tyros and the Motif as well as soft synths, I am already up to my ears in voices I will never use.

The biggest upgrade of the XF as far as I am concerned are the ARPS. Can't get enough guitar ARPS...lol