Since the 4.0 release of the SDA, it is possible to PXE boot both BIOS and UEFI systems simultaneously if your DHCP server allows it.
pfSense has the ability to configure DHCPD to allow this via the web interface
Note: Instructions are based on pfSense 2.3.2-RELEASE
In the pfSense web interface, navigate to Services | DHCP Server.
Scroll down to Network Booting and click Display Advanced.
Please note that the SDA does not support PXE booting 32-bit UEFI firmware, but all three fields must be filled out for UEFI PXE booting to work.
This will update the configuration but the service will need to restart for the changes to take effect. From our testing, it works best to stop the service, wait until it is completely stopped, then start it back up.
This can be done by clicking on the 'stop' button (a square in a circle) icon in the upper right corner of the DHCP Server page. Once the gear is done spinning and the service is stopped, a 'play' button (a triangle in a circle) will show up. Click that button and the service should start up with your new PXE configuration.
Looking at the dhcpd.conf file pfSense generates, the relevant portion of the file looks like this: