These mate http://www.maplin.co.uk/module.aspx?moduleno=2181 i've bought the 4.6R but anything from 3-6R will be fine, you then run them as if they were high impedance (you probably already know all this, but just thought i'd elaborate in case you didnt).

What is interesting is that since fitting the mic cable the only logged run I did saw a RPM spike rather than a drop off like in the pic above, which is the first time i've seen this!