The 8x was part of my old system and I just had the 840C here. Obviously different systems but I have also used the 8SE.
The cyrus'es seem to have more attack but imo leading edge detail is somewhat overemphasised, slightly unnatural. They also push everything slightly forward. Not unpleasant but probably a departure from neutrality though to be precise on that you need to know how the original recording was mastered.
The 840C, apart from a plethora of facilities, not least the ability to utilize the sophisticated upsampling with other digital sources, is more evenhanded, supremely detailed with a lovely pristine and extended treble. There's no grain whatsoever. The better player imo but perhaps better in a more rythmic system.