beyerdynamic does not provide any specific recommendations on products of other manufacturers. However, an important criterion is that the digital/analogue converter (DAC) has high-level inputs, generally implemented with RCA sockets.
As the two headphone amplifiers are of very high quality, we recommend that a high-quality DAC should be used. Both the A 2 and the A 20 are also capable of making the subtleties of different DACs audible