Pro-Ject Tube Box DS vs Pro-Ject Tube Box S

Looking to get an upgrade to my preamp which is currently a Cambridge Azur 551p, and wanted to know what the difference is (sound wise) between these two. It seems as though there has been a price reduction on the DS which I can get for $400 vs the S which is $450.

My current set up is a Pro-Ject Debut III table, Ortofon Blue 2-M cartridge, Jolida FX-10 amp, and Dali Zensor 1 speakers.

Thanks for any insight.