All bad news, I'm afraid. It needs a satellite (or even better a twin satellite) feed. If you can also connect it to your network with either a network cable or Humax's own wifi dongle then you can use the built-in iPlayer and friends.
Sorry, you cannot program it to use an IPTV sub. It uses a closed operating system, and you can't "add apps" to it.
Sky subs with a cline are now dead (Sky have blocked them), you would have needed a sat feed or two anyway, and you still can't add a cline app :)
"FreeSat mode" - the dish points to a satellite called Astra 28.2E (it's actually a cluster of 3, but the dish sees them as one). These broadcast thousands of channels in dozens of languages. FreeSat is essentially a pre-defined selection of channels, and it sorts out the EPG and other good stuff. If you turn off Freesat mode you can receive any channel, but you'll need to manually input each channel's frequency and other parameters, you'll lose the EPG and (I think) you can only record "now" - you won't be able to plan a recording. Note: although you can receive Sky Sports 1 doesn't mean you can view it, because it's encrypted.
Options:
FreeSat / Humax: Ring round a few sat installers for a price for a dish and twin cables.
or
IPTV: Sell the Humax on eBay and buy a dedicated IPTV box and sub.
or
Give the box to me, cos I'm a decent chap.