not trying to pile on but
i too think that the above would cause a feedback loop
atleast the way its currently described
either way u wouldn’t be able to hear what u are doing?
happy to be wrong tho 
the method i’ve been using to record thru ext. fx back onto tape
is splitting the left and right out into separate outs
to create an fx send / return type thing
panning your tape tracks the appropriate way to your ext. fx
with atleast one track panned the other way for recording // monitoring
without any feedback loops
a more in depth explanation from awhile back