SwedeYes you can, the A30 has a switch in the back for the output. It can either be on at all times or only when no headphones are plugged in.
So you could do auto or manual switch over depending on how you configure it.
SwedeI have 2x A30's and a D30, honestly its great especailly for the price.
I compared the D30 vs the SMSL M8 & M8A and honestly its nearly impossible to tell the difference and the level of detail is nearly the same across the boards. I don't think I could pick out either in an A/B.
The A30 has high impedance outputs though so it might vary depending on which headphones you are using and what their impedance is. It did pair nicely though with my Triple and Quad drivers aswell as the Panasonic RP-HD10 (all low impedance headphones).
For the price and volume control you get, I don't think this setup can be beat!
I haven't used the speaker amp because I have no passive speakers as of yet, I might buy it in the future if I get some passive speakers I like.