Choose a saxophone!

[Karl Henning]

I think one could write for soprano saxophone without "looking for that Kenny G sound" about as readily as writing for tenor saxophone without "looking for that Clarence Clemmons sound."  No instrument is limited by any famous practitioner. Not for a proper composer, anyway.

[Wanderer]

I would also go with the soprano saxophone.

[Cato]

I would also go with the soprano saxophone.

Yes!  To paraphrase cartoon character Eric Cartman  "Booo, alto sax!  Booo!"   0:)

[jochanaan]

It really just depends on what kind of piece and sound you want to create. The alto can create lower sounds and can provide more range in certain ways (texture and notes). The soprano can provide more highs and can be more differentiating. It really just depends what you have in mind. The mirimba itself has a wider range, so what you plan for that can be the catalyst for which saxophone to choose. My suggestion would be to go to youtube, enter 'marimba and saxophone', and just listen to the sound of the instruments. You may find this helpful. Both will do whatever you want to do in a satisfactory way.

I suspect our friend Karl is intimately familiar with both the sound and playing of all saxophones and marimba!

I understand that the soprano sax is fiendishly difficult to play in tune, maybe partly the result of its being a 'double' instrument much more often than a mainstay.  (Is this true?)...

It is difficult, but not for that reason.  The smaller wind instruments are just that much more difficult to make good sounds on.  It's all about the pressure needed to play: the smaller the horn, the harder you have to blow (and the less air you use).  Although I've never played the soprano, I have played alto, tenor and baritone, which were easy for me to play relatively well.  (That's one advantage of specializing on the oboe: Everything else is easy by comparison! )  But if a player starts on alto or tenor sax, s/he needs to work harder to make the soprano sound good.