I use the same shoes as yerself (AM40's) and, after experimenting with Wellgos, DMR's, *ank Bros pedals, I found these MN01 pedals by HT components http://www.ht-components.com/ht_portal/product/list?cname=pedal Superstars also do exactly the same pedal.
FWIW, I spent years on SPD's & ATACs, but once I'd learnt how to ride and get air with flats, I realised all SPD's did was to let me get away with rubbish footwork - I'm not a racer, so never really used the 'pull up on the pedal' option that SPD's give you.
Once you've got your preferred flat pedal shoe combo sorted, it's just down to technique, and if an old f*** like me can learn this, anyone can - and (famous last words) I haven't had any shin or calf spiking in about 2 years of regular Peak D riding. Sounds like you're already dropping your heels. Only thing I'd add, is that if you really want to fast forward your technique, get a skills session with a MTB coach that uses flats. Oh, and if you want to get some air, check out MBUK's Doddy's guide to bunnyhopping on YouTube.
HTH