Hi,
Your product does not support simultaneously two 2560x1440 screens.
The majority of DL-3xxx and DL-5xxx based product only support one with a few exceptions like the Dell D3100 and the Targus ACP77.
All docks based on the newer DL-6xxx should be able to support up to two 4kp60 at the same time.
You could get a dock that supports higher resolutions or simply add an adapter connecting it to the docking station. That's the beauty of proper USB video!
We keep a list of product on our website:
http://www.displaylink.com/products
Cheers,
Carlo