which way to start tube-rolling ? please

I don't know about that one. When I went from Sovtek tubes to NOS in my Jolida CDP, the difference was astounding. In my experience, no tube change has been inconsequential. Quite the opposite, in fact.

I went from the stock tubes in my Ah! (w/upsampler) to the Amperex. The improvement was not subtle but obvious. However, as the Amperex in the Ah! is already an 'upgrade" I would suggest rolling some in your preamp before going back to the Ah!

Tube rolling for the Ah! Njoe Tjoeb? Plug in a Scott Nixon Tube DAC. A friend lent me his recently, and the improvement in soundstage and detail was amazing. I ordered in immediately!

I have applied a significant amount of Dynamat and rope caulk to the chassis and transport of the Njoe Tjoeb, and I think this is contributing to it's performance as a transport. It sounds much better than the Sony DVP-S7000 that everyone raves about as a transport.