The Gigaset Box 100 (DE version) is compatible with the Sunrise Connect Box 3 and can be connected directly to it. It supports both analogue and VoIP connections, which enables connection to the Sunrise router.

There is no explicit confirmation in the available information regarding the connection with the Gigaset E390. Gigaset recommends the use of Gigaset HX handsets for the Box 100, as all DECT handsets that support the GAP protocol are basically compatible, but with possible limitations in terms of functions. The Gigaset E390 is not an HX handset, so compatibility may be limited or non-existent.

To summarise:
- The Box 100 DE version works with Sunrise Connect Box 3.
- The Box 100 is optimised for Gigaset HX handsets.
- Compatibility with the Gigaset E390 has not been confirmed and may be limited.

For safe use with the Gigaset E390, we recommend contacting Gigaset customer service or checking the official documentation.