I know it's somewhat dated, but I'd like to share my experiences about these two brands.
While the Pass XA.5 sounded really good, it's no where close to being musical as the Lamm.
I had XA-160.5 and the XA-100.5 and the Lamm M2.2 side-by-side driving Hansen The Prince V2 and Nova Be, the Lamm always sounded more lively and musical.
I also tried some NOS and like the Amprex Orange Globe and Mullard CV2493 very much.