How (does?) SuperCPU 64 control CPU port?

Hi

I'm playing with a project that replaces 6510 chip in a C64 with a Teensy
4.1 board that emulates the CPU:

https://github.com/ytmytm/teensy64

The emulation can be a lot faster than a real 6510, so I plan to put in a
SuperCPU compatibility mode eventually.
The next logical step could be to drop the idea of replacing onboard 6510
and just put everything on a cartridge.

This got me thinking: how does a real SCPU handle access to $01 port?

I guess that SuperCPU's CPLD can track the writes to $01 and update its
internal memory config: providing ROM data from its own copy when needed.
The I/O access might be managed by dropping in/out of the Ultimax mode.

But what about the tape - does that work with SCPU? I don't see any way of
controlling tape from the cartridge port alone, it has to come from 6510
$01 port.

Or perhaps SCPU works using a different principle and the onboard 6510 is
sometimes running?

ytm