This has been debated at least twice recently. I'd run a search for the replies. In fact, I'd always do that before posting a new thread.
From the BS5 perspective - it only really plays digital audio. It's very expensive kit, to play digital audio. I'd buy myself a mint second hand BS9000 and connect an Airport Express. I own both a BS5 and an Airport Express system and the latter is easier to use and more reliable!
The BS5/BM5 is a tad flaky. I've had to reset and reboot the BM5 at least 10 times in three weeks, so far.