Depends on what degree you want to drive them to. I personally find my Atrium to be "acceptable" for portable use with amps at around 400mW @32Ω, because I stop feeling like my music is being suffocated by the lack of power at around this level. I should add that I listen to my music at around 65-70dB typically.
Given that a Caldera's only 60Ω, that's 1/5 the impedance. To get the same level of performance on the Caldera, I'd only theoretically need 80mW of an amp. So for my "acceptable" threshold, a budget model DAP will be more than enough. Now, a higher end DAP will obviously bring better sound quality to the table.
Again, to reiterate others earlier in the thread, the Caldera with its 95mW/dB @60Ω should be relatively easy to drive, and a TOTL DAP should find it a walk in the park to drive. I would say the DAP you choose should be about sound synergy with the cans, than its ability to drive it.