Krell FPB and cast versions

Hi Folks:

Are you really giving up much in the way of fidelity by owning an original series FPB (I am thinking of either the 300 or 600) versus the later cast editions? I don't want to own a Krell pre-amp at this point and I know that's the best cast connection. Any advice appreciated. I own the Thiel 7.2.

Best:

D.H.