Yes, you're on the right track. The setup you're considering is essentially the same as mine and it works great.
There are a couple of things to think about. If you want to use the Music Hall as a one-box CD player you don't need to worry about the number of inputs on the DAC, you'll just plug the Airport Express' Toslink output into the DAC. If you're spending the money on a DAC that will be better than the internal DAC's of the Music Hall you may want to get a DAC that has multiple inputs so that you can use the Music Hall as a transport only and switch between it and the Express.
Some people claim the quality of the Toslink cable between the Express and the DAC is important. I haven't done any critical comparison but I did buy a glass cable rather than the more common plastic one.
One of the issues that is usually raised about the Airport Express is that jitter in the output from it is a problem. If that concerns you you'll want to investigate whether the DAC you're considering deals well with jitter. I've got a Benchmark DAC-1 that is claimed to be almost immune from jitter problems but other can probably give you information about other options.
There are a couple of things to think about. If you want to use the Music Hall as a one-box CD player you don't need to worry about the number of inputs on the DAC, you'll just plug the Airport Express' Toslink output into the DAC. If you're spending the money on a DAC that will be better than the internal DAC's of the Music Hall you may want to get a DAC that has multiple inputs so that you can use the Music Hall as a transport only and switch between it and the Express.
Some people claim the quality of the Toslink cable between the Express and the DAC is important. I haven't done any critical comparison but I did buy a glass cable rather than the more common plastic one.
One of the issues that is usually raised about the Airport Express is that jitter in the output from it is a problem. If that concerns you you'll want to investigate whether the DAC you're considering deals well with jitter. I've got a Benchmark DAC-1 that is claimed to be almost immune from jitter problems but other can probably give you information about other options.