Power and sensitivity should not be an issue for you. The Pass amp needs roughly 1.25 volts input for its full 25 watt output at 8 ohms. Your Topping, at 2 volts max out, has more than enough to drive the Pass, so with your efficient speakers, you’re going to need to be cutting volume quite a bit (unless you are a full tilt all-the-time head-banger.)
So, the question becomes, what is the best tool for controlling the input voltage to your amp? You don’t need any more gain, so that points to a totally passive or unity gain analog preamp. This would allow you to run the digital signal at 100% (no bit loss) but still control the volume to your liking.
Besides the Saga+ mentioned before, Schiit also has a totally passive volume control -- the Sys, for only $49. But, it has no remote. Others have suggested other excellent preamps, though you’d want to consider the gain issue in choosing one of them.