Well for the record, for what it's worth and in case anyone cares I put SAP15n and p in there and they were fine. Biased them according to Enzo's 'turn it down till the mains current draw starts to run away, then turn it up a bit' method. I came across these power darlington types in another amp but I forget which. Not all suppliers have them and usually they only keep the higher-current versions, SAP15 and 18, but it would appear from this experience that these work fine as SAP08 and SAP10 replacements. So there you go.