WM3400 series controllers have two models, as you mentioned.
WM3400 WLAN Controller comes with default 6 AP license, and you have capability to have add-on for additional 30AP license. (Support for 36 AP capacity require version 5.x software)
WM3411 WLAN Controller main differences is that it comes with integrated dual radio access point built into it. Number of AP supported on WM3411 is same i.e. 6 default AP license with ability to add-on another 30 AP license. (Support for 36 AP capacity require version 5.x software)
WM3411 comes with 802.11abgn indoor access point with dual radios (and dual-band).