Quattro LNB 1x vertical low band, 1x vertical high band, 1x horizontal low band, 1x horizontal high band, Quad LNB, 4x universal outputs. I presume that the 4 port you describe is probably the Quad.
Cost of two twin LNBs, not too much different from two quattro LNBs.
Extra DiseqC unit £12
2x Diplexers £30
2 way splitter or amp £5 to £20
So definitely cheaper your way, not as professional, but what the heck, it's for your use. Problem is that I carry out a lot of commercial work, so neatness of solution is important.
There is a quad LNB with integral diplexer available from CPC I think, might be worth looking at, although quite expensive.
This may also be worth a look
http://custom1.farnell.com/cpc/produ...ct%5Fid=264272 , it diplexes a terrestrial signal to 4 lnb inputs