Yeah it looks like Luxman included a nice analog line attenuator so that it could be used in exactly this manner. One word of caution given to those connecting DAC to amp is to check if the volume is controlled in the digital domain. This approach is cheaper but doesn’t yield as good of a result because you can lose some fidelity and raise the noise floor.
I would consider DAC to amp if I wasn’t happy with my integrated.
Mcintosh makes a digital preamp/DAC D150 that would match your MC152.