Hey stewg,
I have nothing but respect for Audio Note UK gear. My hunch is that because all the different Audio Note transports use some type of NOS Phillips transport mechanisms, and the Pro-Ject uses a qualitative new/different mechanism and control board that you still would get a higher level of performance out of your 2.1X Signature by driving it with the Pro-Ject. Part of this hunch is also based on that at least three transports that I have had in-house used different versions of NOS Phillips transports and none sounded as good as the Pro-Ject driving my 3.1 Balanced MK II.
I have nothing but respect for Audio Note UK gear. My hunch is that because all the different Audio Note transports use some type of NOS Phillips transport mechanisms, and the Pro-Ject uses a qualitative new/different mechanism and control board that you still would get a higher level of performance out of your 2.1X Signature by driving it with the Pro-Ject. Part of this hunch is also based on that at least three transports that I have had in-house used different versions of NOS Phillips transports and none sounded as good as the Pro-Ject driving my 3.1 Balanced MK II.