How to choose an attenuator

I have an Oppo Sonica DAC which has 4 Vrms through the balanced outputs and a Classe Amp2 (and a CAV-180 for that matter) which takes 1.4 Vrms maximum input without clipping. I was recommended to use 24dB attenuators to reduce voltage; but this seemed very high to me (based on online voltage to dB converters). Is there another criterion apart from the voltage?
Thanks in advance for any thoughts, as I am not very knowledgeable in this!