Thank you for your replies thus far - they are most helpful.
KG Archery also do Martin Compounds and I've benefited from training by Christine Casgoigne and have shattered all my PBs since that training.
I also found the Alternative site interesting (
Alternative Compound Bows)
not just because they are selling kit but because they have taken the trouble to explain the whys and wherefores for relative newbies such as I.