Do you already have the speakers? If so, just try it. If you don't already own the DeCapos, but do own the amps, I can tell you that a single 30 watt amp should easily power the DeCapos, so a single Aleph 30 should do the job. Try bi-amping, but if it doesn't provide better sonics (to your ears), then you can sell of one of the amps to offset the price of the speakers!
BTW, I've powered my DeCapos with as little as 1.5 watts/channel and it played plenty loud in a mid-sized room. I've also used 3.5 watt, 5 watt and 8 watt tube amps and currently use a pair of Channel Islands VMB-1 mono-blocks at 40 watts/channel.
Enjoy,
TIC
BTW, I've powered my DeCapos with as little as 1.5 watts/channel and it played plenty loud in a mid-sized room. I've also used 3.5 watt, 5 watt and 8 watt tube amps and currently use a pair of Channel Islands VMB-1 mono-blocks at 40 watts/channel.
Enjoy,
TIC