That mirrors my findings with passives. With a 10k pot you ideally want the input on the power amp to be 100k or higher. If not you'll find things sound a tad flat and dynamically squashed. When I ran my WAD power amp as an integrated I used a 20k pot to drive the very high 1m Ohm input of the power amp circuits and it worked beautifully. Take the pot too low though and some sources, particularly tube based or those with poor OP amps in the output stage will struggle. As ever in hifi it's necessary to apply a little theory and common sense.