Most people's opinions on the Nforce 2 vs Audigy 2 is based on firingsquad.com's comparisons, which used ancient Nforce 2 drivers. If you're using the analog outputs on the Nforce 2 your sound will not be nearly as good as the Audigy 2. This is because the DACs on the nforce 2 motherboards aren't very good. However, if you're using digital output there's no reason why the Nforce audio be just as good in quality as the Audigy 2. It would be nice to see an updated cpu utilization comparison with some fairly recent nforce audio drivers.
It seems as if NVidia is improving sound quality on their driver sets. Here's a comparison run from a member of nforcershq.com . Seems like NVidia has gained the edge in certain categories, although the Audigy 2 wins some.
Differences between nForce Audio Drivers and Audigy 2.
I run Right Mark Audio Analyzer in 16-bit / 48 kHz and these are the results:
Frequency response, dB: [nearly to zero is better]
**Audigy 2: +0.00, -0.00
**nForce 2 (5.10.2917): +0.01, -0.26
**nForce 2 (5.10.2934): +0.00, -0,00
**nForce 2 (5.10.2938): +0.00, -0,00
Noise level, dBA: [smaller is better]
**Audigy 2: -97.2
**nForce 2 (5.10.2917): -98.1
**nForce 2 (5.10.2934): -98.1
**nForce 2 (5.10.2938): -98.1
Dynamic range, dBA: [bigger is better]
**Audigy 2: 93.5
**nForce 2 (5.10.2917): 95.8
**nForce 2 (5.10.2934): 98.0
**nForce 2 (5.10.2939): 98.1
THD, %: [smaller is better]
**Audigy 2: 0.0041
**nForce 2 (5.10.2917): 0.0021
**nForce 2 (5.10.2934): 0.0003
**nForce 2 (5.10.2938): 0.0003
IMD, %: [smaller is better]
**Audigy 2: 0.0095
**nForce 2 (5.10.2917): 0.0068
**nForce 2 (5.10.2934): 0.0061
**nForce 2 (5.10.2938): 0.0060
Stereo crosstalk, dB: [smaller is better]
**Audigy 2: -88.9
**nForce 2 (5.10.2917): -93.1
**nForce 2 (5.10.2934): -99.8
**nForce 2 (5.10.2938): -100.4