I've tried a lot of preamps (Hegel P30, Holo Audio Serene, various Rogue Audio RP7 and RP9). My speakers have been Focal (earlier the Scala, now the Maestro Utopia).
The best I've found for the money is the VAC Renaissance Mk V. It is so musical / euphonic compared to the REF6. More important: on my system (Kubala Sosna Elation cabling), I seem to get better bass quality than the REF6.
The cool thing is to actually upgrade from this in VAC world, you need to spend a LOT more (to get the Master). This is why, IMHO, it is fantastic value for the money.
Holo Audio Serene and P30 are a few classes behind.