Should I Upgrade from an Edge G8 amp to the Edge NL-12 amp??

3zub it would really help to know what your speakers are and what you mean by punch? Lacking bass? Or dynamics? Or something else?

Dynamics & punch is probably be the best description. (Sorry, don't have a better description.)  I've rotated between the Totem Forest, Monitor Audio GS10 bookshelf and Aerial Acoustic 5B bookshelf.  So far the Aerials seem the liveliest of the group with the Edge equipment.  They all produce different degrees of bass, with the Aerial producing a surprising amount given the sealed design. 

Looked up your amp and saw a review by Jason Victor Serinus which had the following conclusion:

In a forthcoming revisit to Wireworld and Harmonic Tech interconnects, I shall address in some detail the influence of cables on sound and overall presentation. What is important to say now is that the Edge G8 is an amp for which choice of cabling is a crucial and decisive factor.

When paired with the right cables, the Edge G8 emerges as a fast, powerful amp with excellent bass control, significant detail, and striking highs. Though not a statement product, it offers an enviable degree of musicality that makes it a definite contender for anyone considering power amplifiers in this price range.

Here is the link to the full review complete with measurements:

http://hometheaterhifi.com/volume_11_3/edge-g8-amplifier-8-2004.html

Without reading the whole thing I would ask what cables you are using as it seems this may be an issue with your particular amp.

One other thought looking at all 3 speakers you mention the Ariel 5B you say sounds liveliest and its in fact the hardest of your three speakers to drive. Perhaps whats happening here is your amp, which is fairly high current, just needs a more difficult load to sink its teeth into? Perhaps someone more knowledgeable like almarg might see this thread and chime in with greater insight.