deSilva's reading is "rhetorically" based and places much emphasis on ancient literary technique and context. In many ways this is helpful, but a few times I wonder if he is missing the forest in examining the trees. He comes to 666 and is quick to attribute it to Nero, which is a common reading and perception of the text. This, of course is the gematria technique of reading 666 as Neron Caesar as the "wisdom" required to understand Revelation 13:18.
My most immediate difficulty with this is not unique, but it does seem to continue to hold up a good level of concern. Taking the gematria of 666 as Neron Caesar is to use Hebrew techniques to decipher the defective spelling of a Latin name, all bound within a Greek text. That, to some, appears to stretch it a bit.
However, deSilva does connect this well to the Nero redivivus legend that is present both culturally and perhaps somewhat in the preceding chapters of Revelation. Thus, I think that here is a more thoughtful presentation of this possibility. If John was intending us to see the 666 as Nero, then perhaps he is making the connection to the 666 gematria which also make up the Hebrew word for 'beast.' This might be a strong indicator, but doesn't necessarily give any additional information than John has already shown in his narrative.
In the end, I think that the identification of 666 as Nero falls short. In addition to the stretch of reading that I outlined above, the reading of Nero appears to be quite limited in the scope of Revelation's overall storyline. Revelation 12-13 gives us a trio of grotesque figures which are fairly obvious parodies of the Godhead. This section of Revelation reaches a bit of a climax in 13:18, which would indicate that John is wanting the reader/hearer to connect his call for wisdom to the attached scene.
The Dragon is identified for us as Satan (12:9), and the two beasts which rise from the land and sea (Revelation 13) have characteristics which parody both Christ and the Holy Spirit. The beast from the sea appears to be invincible and looks as though it has survived a fatal blow (at least, one of its heads). Rather than connecting this to the caesars, one should perhaps see that this is a messianic parody, especially in light of Revelation's other imagery and the context of chapters 12-13. The beast from the land goes forth in prophet-like fashion to summon the people of the earth to come and worship the sea beast, just like the Holy Spirit calls for worship of Messiah. And, as the Son and Spirit fulfill the will of the Father, these two beasts work on behalf of the Dragon.
Thus, deSilva's reading might make some good observations but ultimately falls short of the context of Revelation 12-13. Symbolically, 7 is the number of perfection - 6 is imperfect and incomplete. A trio of 7 would be an appropriate number for the developing trinitarian thought which permeates John's apocalypse. Those who use the wisdom which he calls for will see the powers of earth as the gruesome evil that they really are; the people of God will not marvel and wonder at this power.
If 777 is trinitarian perfection, then 666 would be a parody - something which looks legitimate at first glance or naive interaction, but which, upon good and godly reflection, falls short of his glory. This remains, in my estimation, the better answer.