geedub - will do my best!
Are you being charged any fees on your current system (can be hidden in management fees)?
The unit is almost certainly an oldish version of FSD (officially a "Sky" product) but is almost certainly not properly DSO ready - the cabling and amps will probably need upgrading.
FSD is "Free Shared Dish" - this link explains it well:
http://new-channels.com/new/index.php?option=com_content&task=view&id=30&Itemid=46
IRS is "Integrated Reception System" - explained well here: http://www.custom.tv/digitalswitchover/downloads/IRS2.pdf
You really need an IRS system which gives you full channel choice and more flexibility and HD.
To be honest your MA is being a bit of a git. It's up to them to ensure all flats are DSO ready and equipped for Sky+ and in most cases HD.
If you let me know roughly where you live then I can give you the details of a local ASHA (Sky approved installer) who will be able to give a free quote and look at finance options. It often works out much cheaper if managed properly too. We (Sky) are currently doing a national survey on digital readyness - we expect to find that a large number of flats that thought they were ready will only be able to receive a fraction of the channels they should due to old cabling/equipment that needs looking at. A simple engineers signal analysis will identify whether anything needs updgrading.
Hope this helps!