The cable modem is usually a router as well, but we'll ignore that.
Is your intention to get your Foxsat Internet access for the catch-up services? If so, I think you would be best checking whether your cable modem provides router facilities and if not putting a cheap router behind it (or getting a better cable modem).
The key to setting up a point-to-point network connection is to ensure the "peripheral" is manually assigned an IP address which is in the same subnet (in other words group) as the "computer" but does not conflict with any other addresses on the same network (for the purpose of this discussion we shall define the Humax as the "peripheral" - the unit being accessed, and your PC as the "computer" - the device originating the network accesses). With a bit of luck we can do this without altering the computer end.
Fire up your computer as normal. If the cable modem is acting as a router, the PC will request an IP address to be allocated at boot time and remain with those settings until rebooted. As I don't know what the second Ethernet port on your PC does, use the same port and reconnect to the Foxsat using a cross-over.
On the PC, bring up a command console and type "ipconfig" at the command prompt. Amongst other things it will tell you the IP address of the PC and its net mask. The net mask will typically be 255.255.255.0, and I shall assume that it is for what follows.
Bearing in mind I don't have a Foxsat, you then need to enter the menu options and find where you can set the LAN IP address manually. It may be an alternative option to DHCP. With it manual, make the net mask the same as ipconfig gave you, and make the IP address the same in the first three fields as your PCs IP address and something different in the fourth field (eg if your PC is 192.168.1.254 the Foxsat can be set to 192.168.1.100 with net mask 255.255.255.0).
Now you should be able to enter 192.168.1.100 in your FTP program and get FTP access, if the Foxsat has an FTP server, but otherwise unless you have installed the custom firmware and want to access the web interface through your browser I am really not sure what you would gain from this.
However, to use this mechanism to connect through the PC to the wider Internet, you are relying on the two Ethernet sockets on the PC to be on the same network - and they are probably not. Typically they are separate interfaces on a dual adapter so that a computer can be connected to two networks. It is possible there is a configuration option to link them.
If so, for this to work, you will need to duplicate the DNS and gateway IP addresses from the ipconfig list to the Foxsat.