We were in exactly the same position you were in and we considered a number of solutions.
What put us off Sony was that it was quite old technology, we didn't want any potential problems when we migrated from XP to Windows 7, and when Sony sneaked out the rootkit and installed software (without telling the users) onto users computers that disabled certain features and was virtually impossible to remove, well that completely put is off Sony. I personally would never trust them again.
The Sanako solution wasn't the cheapest option we looked at but it was by far the best, as Andrew has already said it actually does far more than the teachers ever use, but I always think its better to have something and not need it than need it and not have it.
The old Sanako solutions used to be hardware based, I remember them installing their own cables for audio distribution, this was to keep network traffic down to a minimum and not disrupt the rest of the school network, but that as technology has improved they have brought out systems that run over your own network cabling, ie you only need computers and headsets. I can personally vouch for the 1200 and the Study 700, it is absolutely fantastic, and loved by both teaching staff and students alike. The great advantage with this is that it is upto date and fully MS Windows compliant.
The other good thing about Sanako is their technical support, they are always helpful and have always resolved any issues we have had.
Gavin