My schedule was crazy-busy this weekend, so my listening notes are based on a very late Sunday evening listening session. I played the following tracks, all on red book CDs:
Miles Davis - Blue in Green
Jacintha - Here's To Life
Dire Straits - Brothers in Arms
My present system consists of a pair of Vandersteen 3A's powered by two Audio Research M100 monoblocks and fronted by an ARC SP-11 mki. Cardas Golden Reference ICs and speaker cables. My living room is approximately 20'L x 15'W with an 18'H ceiling.
Generally speaking, the XA5400es provided for a more expansive sound stage than the 9100es; approximately 20% to 30% greater. Percussion subtleties (Jimmy Cobb's fluttering brush strokes at the end of "Blue in Green", the cymbals in "Brothers in Arms") were easier to discern whereas in the NS9100es, these details were not as apparent; they were more a part of the background. Jacintha's vocals in her track were more spatially expansive; more "breathy" (palpable?) coming from the 5400es.
Prior to obtaining the 5400es, I enjoyed the 9100es in conjunction with the Theta Gen Va DAC. I presently run both setups side by side and I've only had the 5400es since early July and the previous owner put minimal hours on it, so I imagine there's still some break-in left to go through. Eventually, I hope to save enough pennies to get the Modwright upgrades.
On the other hand, the 9100es through the DAC has provided me with many hours of listening pleasure. Seems like well maintained units can be had for a very reasonable amount and can be used either as a great transport or for direct playback. I suppose if the opportunity had not presented itself to purchase the 5400es at a good price, I'd still be perfectly content today with the 9100es-Theta DAC combo.
I'm still working on expanding my SACD library, but I will pull out a few to compare and see if there is anything worth adding to these notes.
Anyway, that's my two cents; YMMV. Happy Listening!