I have the Sennheiser HD 280 Pro. However, it occurred to me, that maybe a sound kit ought to contain more than one production headphone set out in the field; what if someone else wants to hear or monitor the recording, passing the same headphones might not be ideal. Is it sensible to have 2 - or more! - headphones on a project? Also, if you ought to have more than one, should both be the same make/model, so that both (or more) people are hearing the same hardware so one less variable is involved, or is it more sensible to have a different make/model so that you can have a different reference point to eliminate possible bias of a given make/model? For example, I see the Sony 7506 is very popular with the pros, should I get that also in addition? How many headphones do YOU carry into a shoot on any given day? Thanks!