It's going to be difficult to find a good, small,amp w/ DAC for under $500, but not impossible. At this budget I would recommend that you look at a used first generation Peachtree Decco. While it's not as powerful or as refined as the later Nova amp, some folks (like me) prefer the Scott Nixon-designed DAC to the ESS Sabre DAC used on the Nova and later generation products.
If you are looking for a new unit, I would recommend the Nuforce DDA-100 integrated amp. While technically this unit does not include a DAC, the clever PowerDAC design accomplishes much the same thing (but in a different way). I purchased one of these units for one of my daughters to use in her space-constrained studio apt, and she is quite happy with it.
I think that either one of these amps should work well with the JBL speakers that you indicated, although I have not seen or heard this specific model.
If you are looking for a new unit, I would recommend the Nuforce DDA-100 integrated amp. While technically this unit does not include a DAC, the clever PowerDAC design accomplishes much the same thing (but in a different way). I purchased one of these units for one of my daughters to use in her space-constrained studio apt, and she is quite happy with it.
I think that either one of these amps should work well with the JBL speakers that you indicated, although I have not seen or heard this specific model.