Best way to connect Beyerdynamic T90/A20/NAD C326Bee I.A.?

I've been reading the forum and it seems that Tape Out is the prefered way to make this connection. It did not work well for me, the sound was very poor. I've noticed that the A20 has Input and Output jacks that are "looped through, which means audio signals that are present in the INPUT sockets are routed to the OUTPUT sockets, even when the device is switched off," according to the manual. Now I'm not sure about the connection on the A20! It's been many years since I used headphones. I also tried connecting to the PRE OUT on the NAD and it was somewhat better, although there seemed to be an emphasis on sibilants in vocals. I'm not sure what to try next and would welcome any suggestions.  Thanks Bill