Hi,
Try SM Services here in the UK, Terry there is very helpful and should be able to confirm their 8 channel Opto is what you are seeking, their web site is www.smservices.net the opto is in the products/large model section I have used a number of them now without problems and the signal translation is very good when checked on a scope, btw am not sure why you wish to use an opto with the powerbox, I understood(?) that it had built in signal blocking. Mike