geoffsco,
The D112 is made by AKG
The RE20 is made by ElectroVoice
Both are large-diaphragm dynamics, and other mics of that class (which are great on bass amps, in my experience, and so hopefully with your sub too) include Sennheiser 421 (if memeory serves me correctly) and AudioTechnica Pro25. Of these I have only used the 421 and D112, and both did well.
SteveMcB