I dont have a volume control on my amp - I only have a power amp. (If I put a Quad 77 Pre amp back in circuit the quality degrades!) That is the attraction of any Standac - they are the only products in the price bracket that have volume controls and can be used as control or pre-amps.
But I take on board all you say about costs and practicalities.
I would happy to pay £300 - 350 for a fully featured DAC Pre-amp. The nearest competition would still cost three times as much.
http://www.benchmarkmedia.com/system...erter/dac1-pre
But, you have to sell into the market you can work; and there might not be enough folk like me to make it a goer.