That would be overkill, pairing the Titanium HD and Logitech Z5500 speakers.
Titanium HD, like the Xonar Essence, is best used with analogue stereo speakers, or a decent pair of headphones.
You would be using SPDIF connection to the speakers, from the sound card, so the Titanium HD won't be any different from a normal Titanium.
As long as the sound card can do encode to Dolby or DTS in real time, which the normal Titanium can, just as the Titanium HD can, than you're sorted.