Music and Mourning

Originally I had planned to devote a lot of attention to music in this blog, but Asher's accidental death has made it the direct opposite.
One of the strongest restrictions on mourners imposed by traditional Judaism is the restriction against listening to instrumental music, in contrast to requiem masses in Catholicism and New Orleans funeral parades. Musical instruments are associated with the Temple service. The Jews of Yemen never played musical instruments, because they were constantly mourning the destruction of the Temple. Some segments of the ultra-orthodox community of Jerusalem will not have instrumental music at weddings celebrated there, for the same reason. Because in Judaism, instrumental music (as opposed to singing, which is part of the synagogue service, and in many traditional Jewish homes, on the sabbath, people sing special hymns at the table) is associated with celebrations -- weddings, bar-mitzvahs, and circumcisions. Mourners are also barred from taking part in such celebrations.
This restriction was one that I did not observe during the years of mourning for my parents, and I observed it only partially during the month of mourning for Asher. Paradoxically (to digress for a moment), strict restrictions apply to people who have lost a parent for a full year, whereas for people who have lost a child, they apply only for a month. I don't think this has so much to do with the depth of grief one feels for the lost person so much as with the command to honor one's mother and father, though people have offered me other explanations.
During the month of mourning, I did continue to practice saxophone. I didn't want to lose the skills I have been building up for years. I decided to spend a long time doing things that aren't all that much fun. I played a lot of long tones and harmonics, scales, and other technical exercise. I didn't play much actual music, and what I did play was as mournful as possible: the Mingus song in memory of Lester Young, "Goodbye Porkpie Hat," and Ellington's "Mood Indigo." I started associating the Mingus piece with Asher, playing it in his memory.
After the "shloshim" (the thirty days), I resumed my musical activities. I rejoined the big band and started playing again with the improvisation workshop I attend every week.
Music is serious for me, though it's also a great pleasure. Is the pleasure a violation of the duty I have to mourn for my son?
Why did I use the word "duty" just now?
Cultures do impose duties on mourners, like wearing black armbands or immolating oneself on the funeral pyre of one's husband. With respect to the duties that Judaism imposes on mourners, I'm essentially finished with what I owe to Asher's memory. My mourning for him now is not a duty but a constant state of mind, something I couldn't stop if I wanted to, though occasionally I can get distracted, thank goodness.
Even writing in his memory is, partially, a distraction. Music is also partially a distraction but also an expression of what I feel.
My main mood now is apathy and indifference, the inability to get enthusiastic about anything. How can one be engaged in music and indifferent to it?