Ayre CX7e or Resolution Audio Opus 21 OR?

Hi folks. I'm on the hunt for a new CD player. I've narrowed the field but am open to suggestions. I'd appreciate thoughts on the Ayre CX7e and Resolution Audio Opus 21. Anyone compare these units? Can owners of either share their experiences? Also, how does the CX7 compare to the "e" version--is it worth the extra money or should I look for a used CX7? Finally, anyone had their Opus 21 upgraded by Great Northern? If so, what improvements have you experienced and was it worth the money?

Thanks. Rest of the system is ARC 150.2 and SP16 with Daedalus DA-1 and Audience cables.
Would anyone suggest I stay away from the Ayre because my preamp only accommodates single ended RCA's? I'm hearing the Ayre is designed to sound best in balanced mode. Also, how about the Naim CD5x or CDX2? Are they on par with the Ayre or the Opus?

Thanks to all for the help.