They are a drop-in replacement for standard 300Bs. I've used them to good effect in two amps designed for regular 300Bs, as well as in an amp specifically designed for them. I don't know if they will give you more body and warmth, though. The differences I heard were greater linearity, better dynamics and extension as well as a cleaner overall sound. In one case I compared them to WEs and Sophia meshies, in the other to EH.
If I was looking for more body and warmth (which to me says "midrange bloom") I might look in another direction. OTOH, I's suggest you try a pair of KRs anyway, because their other characteristics are so appealing it might turn out that's what you've actually been looking for.
