Alternatively, if you're new to CSN/CSNY and want to know what all the fuss was about here's the collection from the sixties and seventies era you really should own first - it'll cost you around fifty to sixty pounds I guess to get some/most of these - roughly the same price as the extraordinarily over priced 74 live box set. You'll definitely get more long term satisfaction from this list ...
Crosby Stills and Nash (1969) *
Deja Vu (1970) *
Four Way Street (1971) *
Stephen Stills (1970) *
Stephen Stills 2 (1971) *
Manassas (1972) *
If I Could only remember my name - Crosby (1971) *
Songs for Beginners - Nash (1971)
Neil Young (1968)
Everybody knows this is knowhere (1969)
After the Goldrush (1970) *
Harvest (1972) *
Wind on the Water - Crosby Nash (1975)
CSN (1977) - their last great studio album ... *
I've marked with an * the eleven discs I consider the most essential - that includes Massey Hall below .....
later add the Neil Young classics - Time Fades Away (not currently available, maybe never will be), On the Beach, Tonight's the Night, Zuma, Rust Never Sleeps, Live Rust, maybe even Decade and the you've got a great collection. There are a few others which are worthwhile too - other Crosby and Nash studio and live albums, Down the Road - Manassas, Long May You Run - Stills Young Band, Stills (1975).
Also investigate Buffalo Springfield - the box set is nicely priced now and also the Neil Young Archive Performance Series, particularly Live at Massey Hall 1971 *.
That'll do nicely.