I don't really consider myself an audiophile for a number of reasons, but I've always been of the notion that you don't need an enthusiast's wallet to have an enthusiast's mindset. Thus, if we interpret "audiophile" as "audio enthusiast" instead of "someone who throws a lot of money at audio equipment", to me it's about getting the best possible audio quality for the money one is willing to spend.
And frankly, I'm skeptical that the external audio DACs out there can match, let alone outperform, a sound card on the tier of the X-Fi Titanium HD or the Xonar Essence STX within their respective price ranges. I'm sure you can get further improvements with external DACs, but by that point, you're not spending $125-175, but $300-500 minimum, more likely $1,000 (maybe even more).
Of course, it depends on what kind of audio you're aiming for, too. Another possible interpretation of "audiophile" is "someone who wants to be true to the source and hear it as the artist intended".
Pre-recorded music is the most common choice for that, of course...but I'm so obsessed with gaming in general that, if my wallet allowed it, I would certainly collect old DOS-era sound cards and Roland MT-32 synths and other such gear just to make those games sound as they intended. Since there's some on-the-fly synthesis going on, it's no longer just a matter of SNR and THD and other such figures. Even beyond that era, there's the numerous PC games released when 3D sound acceleration, A3D, EAX, etc. were a big deal, and they simply won't let you enable the extra sound effects without the right hardware, at which point you're no longer being true to the source and hearing it as it was intended.
