In a recent job posting Apple states that it is looking for "an Acoustic Engineer who will be responsible for the design and development of many aspects of consumer loudspeaker systems such as Apple’s Hi Fi - including enclosure design, passive and active filter design, transducer design, and design validation."
AppleInsider notes that Apple was once planning a smaller version of the iPod Hi-Fi, the device was set to cater for sub-$200 buyers. But the device failed to come of fruition.