Metal or Carbon Resistors - Which is better?

I'd choose metal film in places like power supplies, more likely to choose carbon in signal path. For most mods I've been using Takman carbon film and/or Texas Components TX 2575 naked bulk metal foils, Takman combo of warmer voicing and precision, TX highest resolving/transparent resistor out there, very neutral, some may hear it as analytical. All these resistors have their place, have to weigh out the recipe.

I too would be wary of using a passive pre with 300B. As for 300B lack of dynamics, depends on power supply and speakers used with, I have absolutely no issues with my monoblocks, each has equivalent power supply to what I see in many stereo 300B. And I've directly compared my 300B amps to my 845 SET from Coincident and Art Audio. 

As for the pre, Coincident Statement pre DHT with dual TVS  I'm running with all factory upgrades and some of my own provides all the transparency, dynamics, voicing, presentation I could ask for. This more sympatico combo than a Pass XP22 I previously owned. Latest Coincident pre runs 300B's vs the 101D's mine runs. Vinnie Rossi also has a very nice 300B I considered. DHT pre's are excellent matches for SET amps.