Tubes will be worse. The rest kind of depends.
The Mini3 is a portable amp, by the way. Do you mean the M^3?
The Mini3 (not M^3) has much worse harmonic distortion at high frequencies with low impedances, but better distortion everywhere else (compared to the E9). IMD is pretty similar. Better noise. Much worse power output, expected because it's a portable amp. Much better output impedance (about 1 ohm vs 10 ohms). Bad crosstalk, little better channel imbalance but neither is very good.
As far as I know CMOY performance is all over the place depending on hows it's made. I don't know specifics.
You want to DIY, make an Objective2. You can wait for the desktop version to be finalized if you don't want semi-portability. The O2 will beat the E9 in most ways, losing out slightly at low impedance high frequency THD and in power output at low impedances where more isn't needed (current limiting, not because of output impedance).