The box itself is capable of 4K. I can't comment about anything other than plain stereo (since that is all I use with it), but I would be surprised it doesn't support some of the basic 5.1 surround via passthrough. However there are NOT many services out there that provide 4K streams. Many claim they do, but many are also "fake 4K". 4K, which has actually been upscaled, or bitrate incredible reduced that 1080p actually looks better. Many services may have a 4K "category" with a few 4K channels but rarely a huge selection. Not saying they don't exist, but most are not. I'd rather see a real 1080p stream with proper bitrate to avoid artifacts, than a crappy 4K with reduced bitrate that just makes me nauseous
Keep in mind that the L1 is the buzz entry level box. There are no frills. Basic IR remote, Linux OS (so no app store or sideloading of other apps), with basic Dual band WiFi and only 10/100 ethernet (no gigabit). Nice box for basic IPTV use, and quite cheaply priced in consequence. But if you are looking for more advanced features, you may want to look for the higher level boxes, like the BuzzTV Classic series. And the recently releases G-Series google certified boxes.