Wireless or bluetooth stero for streaming from imac?
In short, Apple's proprietary version of DLNA, which they call AirPlay, is based on WiFi hardware. Bluetooth speakers, obviously use Bluetooth hardware. WiFi has a far greater bandwidth, so go with that. You shouldn't have any problems.

In theory, Bluetooth could work, but in many implementations bandwidth can be limited, so it's not uncommon for your audio to be decoded from its original format (mp3 aac etc.) by your player (iPod, iPad etc.), then re-encoded to an intermediate format for transfer over BT, and then decoded once again before actual playback.

This extra encoding step obviously degrades the quality. This doesn't happen with AirPlay. Since the bandwidth of WiFi is much larger than any implementation of Bluetooth, even if the audio file is decompressed on the player side, it could be sent to the receiver without any re-compression at all.