You might want to look at the AD8130 amp. It will take the differential output, convert it to single ended and be able to drive the 50 Ohm load just fine. I've personally used the amp a lot and it works well for this sort of application.
You may want to search our product page as there is probably a newer, lower noise, better distortion equivalent op-amp released. But the Ad83130 could suit your needs just fine.
Hope this helps,
Joel
