It all depends what u want to watch and which cams u would like.
I thing the 5900 had serious motherboard issues and was replaced by the 5900+ with Hard drive option. but could be wrong.
personally I prefer the Humax 5400 with additional conax cam route if u can work without HD but I hear new patch does conax (but does it have more timebombs than Matrix/magics did?).
If u only watch 5e and 1w why not save a packet and buy the old stock force 1122s that a certain London retailer is unloading for £149! - new sorftware is rumoured to be coming out for them this week - they not the best but for this money with embedded software cams for via*cc*s and C*n*xand a further 2 slots for cams u can't go wrong.
I hear that @sats and Xtremes are worth considering but I personally have not used either. hope this helps with your choice and good luck.
Keep it Free!