We analyzed the spectroscopic performance of a difference-frequency source that utilizes a 5-W Yb-fiber amplifier for the ``signal'' radiation in order to increase the ``idler'' power generated around 4.3 μm. The amplifier is seeded by a monolithic-cavity Nd:YAG laser at 1064 nm. The intensity noise spectral density of the ``idler'' radiation was characterized. Cavity-enhanced saturated-absorption spectroscopy was also performed to test the frequency resolution. In particular, we observed the Lamb-dip spectrum of the ro-vibrational (0000-0001)R(0)transition of 17O12C16O in natural abundance. To our knowledge, this is the first observation of that transition by the Lamb-dip technique.