HEVC is a standard for compression. A box support HEVC doesn't mean it will support 4k video. You can code any resolution in HEVC. To play 4k video the processor must be capable of doing that. For eg try to play a 4k video in an old PC. All the modern media player support HEVC but when you play it in an old PC it Crashes. To play 4k video efficiently the processor must be capable. If the sundirect HD boxes processors are that advanced , then you can watch 4k. But who will put 4k processor inside a HD box, it will be a wastage of money.