So, actually, I looked up the midrash.
http://hebrewbooks.org/pdfpager.aspx?req=37463&st=&pgnum=69
The conversation with the malachim was only before the jews came out. After the jews came out, they were both able to say shira.
In any event, whether our joy is tempered or not, the ikkar is certainly joy. ????? ????? ????