Stef
As the originator of this thread, I had a good Preamp and was not interested in trying the Pacific without a Pre. Then one day I tried it. I was shocked at how good in my system the Pacific sounded without a Preamp. As a result, I immediately sold my Pre and I am using that money to upgrade to the Lampi Horizon.
I was fortunate enough to attend the soft launch of the Horizon in LA that was attended by Lukasz Fikus. We actually did a A/B comparison of the Horizon with a Pre and no Pre. IMO, I could not hear a difference. Others may have had different opinions. I received feedback from Rob and Fred (NA LAMPI) who attended the Tampa Audio show with Lukasz. They actually did an A/B test at the show and they were using VAC amps. They said the Horizon sounded better without a Preamp.
Given that you have a Pre already, I would go the same route as I did. Try it with a Pre for a long period of time and then try it without. You have nothing to lose and everything to gain especially if you get a Pacific with the Volume Control.
You should get a hold of Fred at North America Lampi and talk to him about his thoughts on Pre or no Pre. In my case, once I get the Horizon, if I am not happy with the sound I can always add a Pre. But I highly doubt that I will. And, it is one less component in my chain.