I would keep the BS9000 as audiomaster. You can configure the BS5 as "no audiomaster". Now you have 5 audio sources: CD, RADIO, N.MUSIC, N.RADIO, A.AUX. Price is fine, if it is in mint condition, including all cables, table stand...
I love my BS9000 too, and since two years I love my BS9000 AND my BS5. BS5 (and MOTS) lets you listen to music in a different way.
In a linksetup with videomaster, you can listen to 3-4 different songs simultaneously. My kids can listen to ACDC and John Mayer upstairs via BS9000 and Beoplayer. My wife can listen to James Taylor via Beoplayer in her office and I can listen to Michael Landau via BS5.
Also works with other songs ....
Stefan