Thanks, yes that is what I was doing, here's a bit of the actual code snippet:
onSelect: function(data){
dwap.page.xref_sel(data);
var wo = $('#XREF').textbox('getValue');
var woq = $('#X_QTY').textbox('getValue');
$('input#QTY').numberbox('options').max = woq; // set max value
$('input#QTY').numberspinner('setValue',woq); // set qty to qty.
After the code executes, I can still increment the numberspinner beyond it's max value.