03-07-11: Almarg
..it would certainly seem conceivable that replacing an hdd with an ssd might affect (and hopefully improve) jitter levels and noise levels on the signal supplied to the dac.
The keys in that senetence are "might" and "hopefully", those are not reassuring words.
When you optimize the computer for music playback the access speed of the drive might be a non issue so controlled test with SSD vs. HDD should be made, one easy way would be to take once Mac mini with regular internal HDD and connect an external SSD. If the external sounds better we might extrapolate that to an internal SSD sounding better, but if the external SSD sounds worse or equal it might be the interface connecting the drive. Since Macs use USB or FW for external I would wager the internal HDD on Sata might outperfom.