It is a very bad idea indeed. All you need is a full amplitude startup "pop" from the DAC and you'll blow your speakers. Use a reputable preamp with sensible start-up muting etc., ideally. The OI of the Hifiberry won't be right for the power amp, and you won't have any of the usual protections that a preamp provides.
I'd certainly never connect a device running a slightly flaky and ill-defined software and hardware stack like this to a power amp- I value my speakers and my ears.
(..software has bugs, even software that you like

)