I had the 108 pre-SCNP connected to a VTL 7.5III preamp and it sounded great. I upgraded to the 108 Model 2 and the improvement was huge. The 7.5III is a great companion to the 108
I've never owned an 18NS but would like to do an A/B comparison with the VTL someday. A audio business owner I know sells Dartzeel, and he loves the 108 Model 2, but feels while the 18NS is a great sounding preamp, there's a lot better bang for your preamp buck out there. He would recommend the the Aeris Cerat line of products, which he also sells.
I've had numerous email conversations with Herve' over the past few years. While @thanasakis has had issues with the Dart, I can't help but feel if Herve' is made aware of an issue, he'll do what he can to fix and improve his product.