Hi Christof,
We tested 4 Intel machines (a Macbook Pro and 4 and 8 core Macpro´s) under 10.5.4 with Logic8.0.2 and Protools7.4.2 (HD and LE) and have not experienced any troubles yet. On the other hand the combination of a G5 with 10.4.11 and VI running in Cubase/Nuendo immediately produced the errors you are describing.
We will investigate this further and have already a new (intern) version for looking into this also during this weekend to solve this asap.
best
christianK