For what it's worth, I tried plugging an Alpha Central via the official adaptor cable, into my Prodigy Advance 2. The buttons light up and you can program the box to match your accessory (points, signals etc) numbers. BUT, while the Prodigy happily operates said points etc, the Central box doesn't, i.e. Alpha Central reads Prodigy but not vice versa, or at least won't pass on the signal to the point motors. So I'll need a Cobalt Box and a transformer to separate points et al from track power.
Pending the availability of the Cobalt Alpha Power module, it would be useful to know the size of plug needed from an alternative power supply unit into a Cobalt Alpha Box. But no further expense until I know the cost and availability dates of the Ally Pally announcements.
On the subject of cost, I reckon a DCC system costing the same as 2 or 3 locos, is probably worth it, as is the option of NOT doing lots of soldering if you're as cack-handed as I am.
And separating track power from accessory power is very much a Good Thing, even if it means you stay with analogue post control.
Richard
P.S. It would also be interesting to know whether an NCE handset, plugged directly into a Cobalt Box, could be used without the rest of the NCE gubbins as a DCC system in its own right.