Exchange Krell KAV-250a for a Pass Labs X-350?

Would you borrow the Pass amp from a local dealer? Try a Pass X series pre-amp first. They are truly balanced - like the X 350. I think the KAV-250a is truly balanced?! You might want to try an Adcom GFP750 pre-amp also. It has single ended & truly balanced inputs & outputs, & was designed by Nelson Pass, who founded Pass Labs. I use the GFP750 with my Rowland Model 2 in balanced mode & it works quite well.
I've seen the NAD pre amp at a local dealer, I believe it is "psuedo balanced" which means although it may have "balanced" inputs or outputs, they are coverted inside the pre-amp to single ended anyway. Check the input & output impedance numbers. The Adcom input impedance measures 94k ohms balanced, 47k ohms unbalanced. Output impedance 1200 ohms balanced, 600 ohms unbalanced. When the balanced value is double the unbalanced value, the component is "fully balanced" or "truly balanced".
I also own a Pass Aleph 3 amp, it is single ended only, when I use it I run the variable out from my SONY XA7ES directly into it.
If I were you I'd give the Krell another chance with a better pre-amp.

Dale, you mention "sterile": to me this sounds like you're questioning the KAVs tonal balance & musicality in yr system. IMO, try the X-350 on this system; listen to light jazz & classical, and check out the X's tonal balance vs. the KAV. You want to be drawn into the music -- i.e. does the Pass render subtle musical details more realistically to your ears? Do the little sounds "make sense", are they indispensable to the musical piece -- or could you have dispensed with them? If they do and are, and didn't and were'nt before, keep the Pass!

Three people I know (who found the KAVs a tad "dry" to their taste) ultimately chose Pass, YBA, Atma-sphere. Pls note, however: COMPLETELY different systems!

Cheers!

Danielk141 You are starting to get into realms that I don't deal with but here but here is the statement for the S-100 manual.
From input to output, the S100's circuits are engineered for very-low-distortion Class-A operation, with a vanishingly low output impedance (long an NAD hallmark) that reduces the sonic impact of cable impedance to near insignificance. And it provides a choice of primary outputs: conventional, unbalanced RCA jacks, and fully balanced XLR jacks. Unlike those in many consumer products, the latter are true "pro-audio" outputs capable of delivering up to 20 volts to 600-ohm loads while significantly reducing susceptibility to external hum and noise.
Maybe you can interpret that. I listened extensively to the Adcom GTP-750 since I owned Adcom equipment before this system. I felt that the NAD was just much more smooth and balanced to my ear. I also discovered during testing different gear that I like the balanced connections between the preamp and amplifier but the single ended connectors between the CD player and the preamp just sounded better.
So what I am getting from most is that there may be a difference in amplifiers but the real difference is in the preamp in my system. I have been listening to a Sim Audio Moon P-5 and was thinking about taking it home soon but I have not heard that much from it that would make me think that I am lacking at home.
GregM, when I am speaking of sterile due to a lack of tonal balalnce, I am repeating what I am hearing from some. I am not stating that I hear that. But I am wondering if I am missing something since I don't know any better. You don't know what you are missing until hear it in something or some where else. I tend to like my listening a but more analytical (favor SS ) than smoothed out (tubular) so I will favor towards something that seems to sound more accurate than something that may sound more musical but lacking detail. So I have to like the sound. My mileage does vary obviously. Dale

Most pre amps with a balanced input and output will have impedance specs simular to the ones mentioned. In a balanced output stage the designer will put protection resistors on the outputs and the value doubles because now ther is two of them in a balanced configuration.

The input and outputs being balanced will quite often double the impedance specs but that does not mean that the input stage did not convert the signal to single ended. The signal then gets processed just like any other pre amp and then gets converted back to differental in the output stage. A fully balanced design has a four gang volume control vs a dual unit for a single ended design. There must be twice the gain stages in the fully balanced design. I hope this clears up some confusion. Chris

Dale,

Ok, you got me there.... I didn't realize the Silverline was a different product line. I've owned other NAD products in the past (cd player, amp, receiver) and found them to be good values, but not "high-end". now I know something new.