I had the same problems trying to install Logic Studio Pro 8 using its original DVD's.
I solved the problem extremely easy and without any Terminal commands or workarounds:
Using you SNow Leopard Install DVD install Rosetta (found under "Additional Software") into Lion. Reboot and after that Logic Studio Pro 8 will install without any errors.
I've been using it after this install for a couple of months now, without any workarounds, errors, lost plug-ins and so on, whatsoever.
Hope it helps
Patrick.