"DLS" is "Dave Liebman Signature," introduced in 2011/2012. I quote from the Saxquest website:

This soprano was developed by a collaboration of Dave and the Keilwerth team.
The SX90 DLS is a cutting edge soprano saxophone which features specifications and designs set by Mr. Liebman.

These sopranos have a larger bore dimension which allows for a bigger more enriched sound, very warm in color.
The enlarged side keys in the right hand also make it possible for you to play the alternate F# and high F# key with the inner side of your fingers in addition to the traditional fingering method.

The SX90 DLS also includes a number of cork pads in areas traditionally occupied by leather.
Cork pads allow for a more positive feel and longer lasting durability.
The cork pads are a huge positive for the performance of the soprano, especially in the upper register where things can be more suspect for difficulty.

Like all SX models by Keilwerth these sopranos also features adjustable palm keys.

In our opinion this is one of the very finest sopranos made today. It is an incredible horn!

Keilwerth promo video.