I see several Further guitars for sale online. Among them in Quilted Maple, there are two styles, Further and Further Studio. What's the difference?

Where do you see a Further "studio"?
My best guess without actually seeing the listings is that it is just the wording the seller decided to use. I don't believe there is such a thing as Further studio model.

there is a furthur stage
https://alembic.stores.yahoo.net/stagefurther.html

Quote from: jazzyvee on July 31, 2019, 11:27:22 AM
there is a furthur stage

My mistake, Stage not Studio.

https://reverb.com/item/24602947-alembic-further-stage-electric-guitar-excellent-2009-ohsc-free-shipping?gclid=CjwKCAjw-ITqBRB7EiwAZ1c5U6zGYRr5hdLyc443WJX28yFCaxUcBX4l8FUfr37fsTyLZOqkdxiqkxoCwJIQAvD_BwE&gclsrc=aw.ds&merchant_id=117072678&pla=1&utm_campaign=673000280&utm_medium=cpc&utm_source=google

It looks like the Stage Further's have an FJ serial and do not have a back lamination matching the front. Like the difference between a Standard and a Deluxe.
Both examples referenced in the thread (the one featured here on Alembic's site and the one on Reverb) share these traits.
They also have different controls including a 5 position switch with brass plate and one of them has a brass pickup surround.
Whereas, regular Furthers have the same control layout as Tributes.

Also found this:
http://alembicguitars.net/club/messages/393/62726.html?1238618387

"Here it is... your "beater" Further :-) Well, maybe that's a little bit of a stretch, but at more than 30% less than the original Further guitar, it might feel more comfortable taking to some venues that a custom Further guitar might be too shy for.
The Further Stage guitar features a friendlier set of controls for live performance. A simple volume and filter control with a 5-way blade switch for fast pickup selection is all you need. To get even more from your outboard effects units, effects loop operation is with a blend control, to mix just the right amount into your sound. " - Mica

Thanks, y'all!