As far as I know, the Titanium HD uses an NJM4556 op amp (surface mount version) to drive the headphone output. The same chip is also in a number of other Creative/E-Mu products. It is actually fairly well suited for driving headphones, and is also used in the O2 (two DIP8 NJM4556's in parallel for increased current output and power handling). However, the Titanium HD does have a relatively high, ~35-36 Ω output impedance.
It is a common belief that only "hi ohm headphones" can be difficult to drive, while low impedance ones can be safely plugged into anything with a 1/8" jack, but it is incorrect. In fact, other than the amount of voltage required for the same power, low impedance is harder to drive in every way, and line outputs are often not designed to handle it. A line input typically has at least several kΩ impedance, compared to that, a 32 Ω headphone is like a short circuit. It may still be driven to usable volume, but possibly with increased distortion and frequency response problems.
Edited by stv014 - 3/1/13 at 4:51am