Is there Really a difference between a Krell 400xi intergrated amp and the newer Vandgard?

I  believe I  will call my personal friend Patrick Bresnahan's personal cell phone and talk with him about this vanguard,  and see what modds are possible that can be done with the vanguard.

if vanguard so great,why there is for sale some used ones?:) And not so much krell fbi?I actually can’t find krell FBI for sale. I have krell kav500i.quite a good amp,indentical sounding like krell 250A and 250p combo,bass and soundstaging,espcially vocals are spot on

I would be interested in reading about Krell mods.

Very few FBI's were sold.  The FBI was an FPB 300 and a KCT in one chassis!  Quite a few Vanguards were sold and at any given time many great pieces of Krell and or other top brands are listed.  That said, Krell could have put line level outs.

I have owned several stacks of Krell gear dating back to 1994.  This goes back to an original KSA-150, KSA-300S, a beautiful pair of KAS-2's, 450MCX's with KCT and Cipher.  As far as integrated amps go, I have owned the 300i, 400xi, and FBI.  I used a Vanguard for six weeks that belongs to a friend of mine.  It is head and shoulders a much more refined product than the 300i and 400xi.  It is definitely voiced differently from what the original Krell "house sound" once was.  I know that herndonb indicated that the Vanguard "wallops them all".  Perhaps is does wallop the 300i and the 400xi! Does it wallop the FBI?  Absolutely not.  I'm not sure what kind of speakers or other ancillary equipment was used, but the Vanguard is by no stretch of the imagination in line with the FBI.  I've played both amps through Eggleston Works Andra III's, Martin Logan Summit X's, and Wilson Audio Duettes.  As good as the Vanguard is, just how good it is depends upon what context you are using it!