KAB RF-1 connection

I don’t know if the MA6900 has one. I am using McIntosh separates. You can use the tape loop if you have one, same thing as the processor loop. 

I wish I had one.

I am sorry what is a process loop? Does the MA6900 have that ? 

I use mine on a processor loop on my Mac preamp.  I play through the moving coil input and engage the processor loop when I want to use the filter.  I have had mine for at least 8 years, it’s loaded with audiophile parts.  A tape loop will work.  Don’t put between the preamp and amp because then you will be using it all the time.  Don’t forget to plug it in.