All these list below $1000, but with the Benchmark DAC you would need to factor in the cost of a transport, especially if you were planning on selling your Marantz 5001 or using it in a second system. I haven't heard any of these, but I was thinking of taking advantage of a home trial of the Benchmark directly from the manuf. http://www.benchmarkmedia.com/dac1/
Also, www.musicdirect.com has the Rega Apollo (and the Marantz) and a 30-day return policy, however, most Rega dealers are restricted geographically so I'm not sure whether music direct is restricted to local sales. Spearit Sound and Underwood HiFi are reputable Jolida dealers and may allow you to return the JD100A if you're not satisfied.

Jolida JD-100A - tube output and headphone output - with new production 12AX7s improving in quality and sound at afordable prices, this one could probably keep one's interest for a while. Mods available.
Benchmark DAC1 - pro quality headphone output. Can be used as a dac/preamp for your cdp directly to power amp or power amp section of integrated.
Rega Apollo - 4 levels of error correction, Wolfson chipset and many rave reviews decribing it as "barrier breaking" for price. You might not need to open the top loader lid all the way to change discs which may give you the room you need on your rack. (You could place a piece of felt or something soft with adhesive backing on the underside of the shelf above the cdp where the lid would strike.)
Marantz SA8001 - SACD and "about as good as Redbook gets."