Does USB cable length make a diference?

No.

The Tivoli... funny. I bought one of those for the kitchen... I gave it away.

Yes, separates of the same quality outperform an integrated. Putting all those circuits so close together generally degrades the performance.

In general, interconnects and speaker cables... shorter is better. But they must be long enough to do the job. High quality ones don't degrade the sound as much as budget ones. 

Power cords are different. Longer the better. 2 meter being the preferred length. I was able to test a one and two meter of the exact same model on my power amp... it was very obvious. As my dealer says, "Twice the length, twice the power conditioning."

Not in my experience. The quality of the interconnect. I spent about ten years upgrading my headphone system from basic PC and iPod then streamer to high end headphone amps. The quality of the interconnect made a very big difference but not the length.