Thank you cgtrox, very helpful - the more I read about them the more paranoid I became about blowing up my amp. I play in an apartment and am pretty happy with how my amp sounds just on low volumes but will look forward to being able to crank it a bit more for some tube action when I get an attenuator. I've actually ordered the Reyes Output Tamer 8ohm so I guess I got lucky with that. Thanks for confirming that it was the 8ohm one I needed. I'll give it a go and if I'm not happy will try out the Weber 50watt Mini Mass which also seems like very good value (the Reyes one comes with a 30 day guarantee).

For anyone else out there thinking about an attenuator I'll post a review of the Reyes Output Tamer when it arrives.

PS I love how efficient this community is, I posted my question before leaving work and had the reply waiting for me when I got home. Nice work.