I think the Seductor is a really nice design and I've a personal love for the EL84, but it should have a volume control IMHO so it can be run on it's own. If I buy a Seductor and even just a Submissive passive attenuator I'm into more money than a Stereomour. Add to that an extra interconnect.
Why not have a hole punched in the chassis (with a plastic plug) for a volume control and offer the volume control as an option?
Question: Can I use a headphone amp/DAC (2.4 VRMS max output with an output impedance of .2 Ohms) as a preamp straight into the Seductor?