There is a big difference between multiple IDE expansions in an A2000 and the mainboard IDE of an A600 or A1200.
The former do Autoconfig which lets the OS assign a different memory address to each expansion. The latter just appears at a fixed memory address.
And that's your problem: both the Minimig and the TF mimic the onboard IDE at its fixed memory address. As the CPU is on the TF, it takes precedence and overlays the same address of the Minimig. You cannot use both at the same time.
