I would get a used Classe Sigma SSP over a used Krell Foundation. Krell as a company isn't the same anymore since Dan D'Agostino's departure from the company in 2009. The Classe Sigma SSP sounds better than the Krell Foundation especially in two-channel performance for stereo music playbacks.
The Classe Sigma SSP is optimized for stereo performance for music playbacks. But the surround or multi-channel performance for HT is very good as well but its stereo performance for 2ch music playbacks that stands out.
I've heard both processors in the same setup and system and the Classe Sigma SSP sounded better especially in two-channel for stereo music playbacks.
For stereo digital music files playbacks the Sigma SSP's USB DAC input port sounded significantly better than its other digital inputs. This unit is optimized for its use of USB DAC input signal path for digital music files downloads. Its USB DAC inputs circuitry was copied and pasted directly from Classe CP 800 stereo preamp/DAC. You can read more on that online to find out.
The Classe Sigma SSP original retail price is cheaper than the original retail price of the Krell Foundation. I think the latest version of Krell Foundation retails for somewhere between $7k to $7500 and the original or first version of the Krell Foundation retails for maybe around $6500, whereas the Classe Sigma SSP version 1 (original version) retails for $5k and the Sigma SSP Mk2 retails for $6k and will sound better than the Krell Foundation especially for stereo music playbacks or when used as a stereo preamp.
However, the Krell Foundation has more connections eg inputs & outputs connectivities than the Classe Sigma SSP. The Classe Sigma SSP is stripped off unnecessary inputs and outputs connections. You won't find any legacy analog video connectivities nor multi-channel analog audio 7.1 inputs on the Classe Sigma SSP. But the Sigma SSP has a pair of stereo analog audio inputs (both XLR & RCA). And the analog audio outputs on the Classe Sigma SSP has XLR balanced outs only for its front LR channels only and with the remaining channels are only available in single-ended but the optimized ones.
The Classe Sigma SSP internal circuitry is true differential or fully balanced design all the way for only its front LR channels and with the remaining channels are single-ended design.
The Krell Foundation processor has all XLR analog audio outputs for all channels but not sure if its internal circuitry is true differential or fully balanced design all the way like the Classe.
For stereo music playbacks the Classe Sigma SSP also sounded better than any Anthem processors, but the Anthem has advantages in multi-channel or surround sound applications for HT cause Anthem's ARC (Anthem Room Correction) is very good and really works.
Especially the new Anthem AVM60 processor is equipped with the latest ARC2 and performs very well in surrounds for HT and is better than the Classe Sigma SSP in that regard.
The Arcam processors are good too.
The Classe Sigma SSP is optimized for stereo performance for music playbacks. But the surround or multi-channel performance for HT is very good as well but its stereo performance for 2ch music playbacks that stands out.
I've heard both processors in the same setup and system and the Classe Sigma SSP sounded better especially in two-channel for stereo music playbacks.
For stereo digital music files playbacks the Sigma SSP's USB DAC input port sounded significantly better than its other digital inputs. This unit is optimized for its use of USB DAC input signal path for digital music files downloads. Its USB DAC inputs circuitry was copied and pasted directly from Classe CP 800 stereo preamp/DAC. You can read more on that online to find out.
The Classe Sigma SSP original retail price is cheaper than the original retail price of the Krell Foundation. I think the latest version of Krell Foundation retails for somewhere between $7k to $7500 and the original or first version of the Krell Foundation retails for maybe around $6500, whereas the Classe Sigma SSP version 1 (original version) retails for $5k and the Sigma SSP Mk2 retails for $6k and will sound better than the Krell Foundation especially for stereo music playbacks or when used as a stereo preamp.
However, the Krell Foundation has more connections eg inputs & outputs connectivities than the Classe Sigma SSP. The Classe Sigma SSP is stripped off unnecessary inputs and outputs connections. You won't find any legacy analog video connectivities nor multi-channel analog audio 7.1 inputs on the Classe Sigma SSP. But the Sigma SSP has a pair of stereo analog audio inputs (both XLR & RCA). And the analog audio outputs on the Classe Sigma SSP has XLR balanced outs only for its front LR channels only and with the remaining channels are only available in single-ended but the optimized ones.
The Classe Sigma SSP internal circuitry is true differential or fully balanced design all the way for only its front LR channels and with the remaining channels are single-ended design.
The Krell Foundation processor has all XLR analog audio outputs for all channels but not sure if its internal circuitry is true differential or fully balanced design all the way like the Classe.
For stereo music playbacks the Classe Sigma SSP also sounded better than any Anthem processors, but the Anthem has advantages in multi-channel or surround sound applications for HT cause Anthem's ARC (Anthem Room Correction) is very good and really works.
Especially the new Anthem AVM60 processor is equipped with the latest ARC2 and performs very well in surrounds for HT and is better than the Classe Sigma SSP in that regard.
The Arcam processors are good too.