Update 2: I obtained the design white paper from Sony regarding the XA5400ES... As a side note, this paper should have been peer-reviewed as it contains many contradictory statements, and hints to the player having multichannel analog outputs, which it doesn't. However, it clearly states that CD upsampling is performed by the DAC IC, the DSD1796 from Burr Brown. The datasheet for this IC is available here.
As one can see in the datasheet page 8, the CD upsampling filter is a "regular" half band FIR filter; recent developments in digital filtering points to the pre-echo of that type of filter to being detrimental to sound quality, in particular sibilance (countless papers available on the AES). There are several alternative approaches to fix this issue: one of them is to use IIR filters instead of FIR, at the cost of a lot of phase distortion. Another approach is to use a "minimum phase" transform FIR filter, which translates the traditional symmetrical impulse response to asymmetrical at the cost of some phase distortion. This enables the designer to trade off pre-echos and phase to the optimal blend. The results are quite evocative, with better high-frequency extension and integration, especially when vocals are recorded with a large amount of high-frequency content. This filtering technique is in use in the Wolfson WM8741 DAC, but also in some outboard DACs such as the Cambridge Audio MagicDAC II (in conjuction with Anagram Technology Q5 upsampler), where the user can select his favorite upsampling method.
The SACD section of the player does also use a symmetrical FIR filter, but the very smooth LPF response required for SACD filtering enables the use of a very short sequence with limited pre-echo duration (see p. 39 and 40). This would explain why the 5400ES is so good at playing back SACD, but CD playback shows a slight hint of high frequency grunge. It is small though, and will be noticeable only compared to the best players out there.
All in all, it is a very good player. You would have to spend much more to get to this level of quality, and this is true for both CD and SACD playback. But it is possible to find a better CD player out there- it'll cost you though!
As one can see in the datasheet page 8, the CD upsampling filter is a "regular" half band FIR filter; recent developments in digital filtering points to the pre-echo of that type of filter to being detrimental to sound quality, in particular sibilance (countless papers available on the AES). There are several alternative approaches to fix this issue: one of them is to use IIR filters instead of FIR, at the cost of a lot of phase distortion. Another approach is to use a "minimum phase" transform FIR filter, which translates the traditional symmetrical impulse response to asymmetrical at the cost of some phase distortion. This enables the designer to trade off pre-echos and phase to the optimal blend. The results are quite evocative, with better high-frequency extension and integration, especially when vocals are recorded with a large amount of high-frequency content. This filtering technique is in use in the Wolfson WM8741 DAC, but also in some outboard DACs such as the Cambridge Audio MagicDAC II (in conjuction with Anagram Technology Q5 upsampler), where the user can select his favorite upsampling method.
The SACD section of the player does also use a symmetrical FIR filter, but the very smooth LPF response required for SACD filtering enables the use of a very short sequence with limited pre-echo duration (see p. 39 and 40). This would explain why the 5400ES is so good at playing back SACD, but CD playback shows a slight hint of high frequency grunge. It is small though, and will be noticeable only compared to the best players out there.
All in all, it is a very good player. You would have to spend much more to get to this level of quality, and this is true for both CD and SACD playback. But it is possible to find a better CD player out there- it'll cost you though!