Ideally, you would use a hi-bit (such as a 32 bit) DAC with built in digital volume control, with an output voltage that is similar to the input voltage of your power amps sensitivity for full output. The digital volume controls on these newer high bit DACs are much better than the digital volume controls on the older lower bit DACs that often led to bit stripping which compromised sound quality. The standard voltage output for CD's is 2 Volts, for HDCDs 2.2 Volts, single ended via RCA's. While true balanced transfer has it's advantages, it also typically doubles the output voltage and finding an amp with 4 to 4.4 Volt sensitivity for full power output into it's balanced inputs could be quite challenging. Single ended RCA amps with a 2 to 2.2 Volt input sensitivity for full output is a much more likely find. Having such an arrangement will allow for the amp to output all the power you paid for, while minimizing the volume attenuation and the potential for bit stripping that can otherwise occur with such attenuation. As a plus it will give you greater range of the volume control and make volume attenuation less delicate and fussy.
Your Classe' amp has an input sensitivity of 1 Volt for full output. While a high bit DAC will ordinarily have lots of extra bits to spend on attenuation without bit stripping into many amps; that 1 Volt input is pushing things a bit. It might work for you, but I offer no guarantees.
While not as ideal, using a passive volume control such as a LightSpeedAttenuator between your source and amp with short, low capacitance interconnects could work quite well in your circumstances.
