You need two matched LDRs per channel to emulate a potentiometer. If you have 6 pairs that all match each other you can control them all easily with one potentiometer. If you have 6 pairs that have matched pairs but the pairs dont match other pairs you will have balance issues which can be sorted out by giving each pair its own personal control potentiometer. The only problem here is that it gets fiddly to have to turn up your volume with maybe one major control pot and then fiddle with each of six other control pots to get the balance right.
SO, if you were to buy LDRs to match for this project I would suggest buying them from me as there is NO WAY you will ever get 6 pairs that all match until you are into the hundreds of LDRs in matching. However if you wanted to match your own and just get 6 pairs that you would need to use balance pots with you could buy maybe 50 LDRs and accomplish this very easily.
For a balanced set (thats 4 pairs that all match) I charge 100.22 including shipping and all paypal fees, etc. For a regular single ended set which requires 2 pairs I only charge 38.42. Why more for the balanced? Because they are more rare and harder to find in a batch of matched LDRs. So 6 pairs would run you 171.28. I think you might be better off if you bought your own for matching or if you bought 3 single ended sets and just adjusted balance between 3 sets.
Just my suggestions. I hope this works out well for you. You will certainly be the first 6 channel Lightspeed I have heard of

Sent you an email. I am planning on building and LDR attenuator and has been reading the very long thread at diyaudio.com.