No. the S-series Performance data is not compatible with Montage.

Do not read or motif of the XF performance

Although not directly compatible: previously instructions were given to first convert the S[7,9]0XS file (.X2E) over to a Motif XF file (.X3E) using existing tools.

See: https://www.yamahasynth.com/forum/loading-x2e-files-into-montage#reply-13722

Yamaha's compatibility FAQ online is a broken link:

http://usa.yamaha.com/products/music-production/synthesizers/montage/#tab=PD5126717

Is there any data compatibility with MOTIF series?

Yes, MONTAGE has the Voice compatibility with MOTIF XF.
And also has some compatibility with old generation MOTIF series. For more detail, please check the following URL.

Data Compatibility with Yamaha Synthesizers

Although broken in the US, Canada still has the page up:

http://ca.yamaha.com/en/products/music-production/synthesizers/montage/#tab=PD5126728

Which now needs some updating with the new MOXF compatibility.

Thanks Jason, that is big help. I can do that!
I've been so ambivalent about Yamaha's new miracle keyboard (Montage)
The feeling from playing its piano (on the 88-key model) is sublime. It's perfectly responsive.
The other sounds are, to my ears anyway (so far) almost a bit too safe and perfect (except for the bent FM of course. And the Rhodes! And maybe the B3 with a bit of tweaking...and those horn articulations...and one of the string sounds I heard....and...)

And with my beloved s70xs (and new little favorite MX49!) I couldn't justify further consideration of its big weight and large (but fair) price point.
I haven't found a nylon guitar patch on the Montage (not year anyway) - (in the stores or on youtube) that matches what I tweaked on the s70xs in terms of bite, softness and playability; but since I can import sounds, using XF format as an intermediate stage, and 2 librarians....and I'd have all the other Performances I've been putting together on the s70xs over the past year and a half....and since 44lbs (s70xs) is STILL too heavy for me to cart around town...what's another 20 if it's gonna be sitting in my studio in front of a computer anyway? (and of course, with the new 1.50 Save All back line usefulness, once i'm back on the road (read:NEVER!)...)

Ultimately, the curiosity - of just what an old guy like me, an 80's DX7 tweaker, and longtime Motif user, could discover and share, with the advanced fruits of all of Yamaha's cumulative expertise and wisdom - plus knowledge that I'd be granted access to state-of-the-art sounds and sound quality - combined with a Reverb.com price that almost seemed like a typo - was just too much to fight.

So the new journey begins when it arrives.

Compatibility does NOT include S90XS/S70XS PERFORMANCES or Motif XS/XF PERFORMANCES... Compatibility is limited to Voices and Arpeggios from the S-series and additionally, Waveforms for Motif XF. Not Performances. You would need to rebuild the Performances by selecting the same sounds for Parts of the Montage. There is a fundamental difference in how Performances function in the previous products.

For example, in you S70XS the Performance only references a Voice location in either the Preset or User Bank. Say you build a S70XS Performance using custom User Voices... It is possible, in the S70XS, to load a different USER Voice bank and have all your Performances point to the wrong Voices. This cannot happen in the Montage because the Performance contains the actual data. There are no "pointers" to other locations, each Performance contains its own unique data.

Thanks Bad Mister. So after I have the Voices moved over, I will have to group them as Parts into a newly Initialized Performance, and reenter their old (s70xs) Performance Settings, such as the four faders' four parameters, and the four knobs' top four (Tone, EG, EQ and Effect) - and maybe some effects settings. (I'm less dependent on Arpeggia than some.) Can do. Much appreciated.