If you are using an older Revision of our switches (Rev A through C) just plug the AF5X into a port that is capable of 48VH
"but select standard 24V as the POE option for that port" as those special ports that are capable of 48VH have .75A Poly Fuses and even though you are using only 2 pairs you can safely go about 150 feet of cable with a .75A Poly Fuse on only 2 pair.
Now if you have a new Revision D board then you get .75A on all standard 24V and 48V ports so it does not matter which port yo use so long as the cable is less than 150 feet.
All of the WS-8-250-AC switches shipping now are Rev D except the Pre-Production units with the WHITE Decals were Rev C.
You can tell what revision your board is under the Device/Status Tab but on firmware v1.2.0 or newer it tells you what each port is rated at under the Ports Tab where you select the POE for the port.Now both the WS-6-MINI and the WS-12-250-AC now support 24VH which is 1.5A on all for pairs on special ports. On the WS-6-MINI that is port 2 and on the WS-12-250-AC that is ports 1-4.
THe WS-12-250-AC will start shipping tomorrow but seriously any of our switches will power the AF5X, many have been powering AF5x for months, go read this post
HERE