That Questions per Day number is a problem, and while we are not allowed to go into detail on the analytical data, this seems to be down to not getting enough new users in.
Our total page views and number of visits are increasing and the curve trend is upwards, which is excellent, but our new user graph is pretty flat. I think we'll have trouble hitting the threshold until this picks up - simply to be able to get enough questions per day. The upside is we are growing, slowly, and as the SE devs remind us we can stay in beta for an extended period, as long as it looks like we can keep growing. Interestingly, we are getting lots of new visits - so one problem seems to be the conversion ratio.
In trying to remember similar points in Sec.SE's history, we did a strong piece of publicity work (actually a few) identifying hot topics in security in the news or on the internet and making sure we had posts about them linked from blogs etc. thus ensuring we built credibility on a lot of sites.
Music.SE is going to be a different beast, but we could do something like have some questions related to Eurovision (yes, I know...but it has a large audience, so piggybacking off the #eurovision hashtag would be not necessarily bad) or SXSW or around popular music (I am a bit of a fogey here, with most of my favourite bands dating from the 60s and 70s so pop music isn't really my forte, but if a popular artist has some special technique or style that could make a good topic)
Active voting is also essential - not only to help encourage good questions and answers, but also to enable a higher number of 10k members of the community.
As a reward for voting, we have the shiny Electorate badge - which only two people have so far (@MatthewRead and @luserdroog) earned here! We don't seem to get many highly voted posts on Music.SE. Perhaps our regulars should revisit older questions and check for posts which deserve upvotes, or ones which could do with better answers.
Update 30 Aug 2013 Did some more thinking on number of visits. As I moderate two other sites, I can do a read across of how we stack up, and I have a couple of points to note, without giving away too much of the in depth statistics:
On Security, by end of private beta we already had more visits per week than Music has. In remembering back to those times, the core things the entire community did was to tell their friends, encourage posts on bulletin boards and forums and generally encourage people to come and check it out. A large number of those people in security also use computers as part of their day job - so it is easy to get them involved here. A large number are active across the Stack Exchange network.
On Music we have a small core of active users, almost all of whom are active elsewhere on Stack Exchange, and then a much larger number of occasional visitors who have no other SE accounts. These feel to me like non-IT folks, so our challenge here is how we make this site as welcoming as possible to them.
I think our scope is correct (despite the occasional post suggesting we allow 'who is this singer' type questions) - but can we target music schools or music theory and practice courses at colleges and universities, maybe?
Also, everyone follow the StackMusic twitter account and retweet good tweets!