"Based on your advice I purchased a Stello 3 however the Squeezebox Transporter does NOT have a USB output to go into the Stello. Does this mean I wasted my money based on your advice or am I incorrect?"
That device looks like it is designed to go from computer USB to DAC.
If your device (Transporter) does not have a USB output, I think you are out of luck.
My recommendation would be always check device interfaces for compatibility, especially in the computer audio world BEFORE BUYING else these kinds of things are quite likely to happen.
These things happen along the way sometimes. Its a learning process. I'm sure many of us have made similar mistakes.
A vendor satisfaction guaranteed or return policy of some sort is always good insurance, especially if a major investment is involved.