Hi,can i use selfpowered speaker with usb dac?

I have Kurzweil ks40a speaker(20k ohms) and topping tp30 usb dac(4-8 ohms).

Thank you.
I took a look at the documentation on those models. I suspect it will work ok if you connect the Line In "B" jacks on the main speaker to the headphone jack on the DAC/Amplifier. It appears that the audio connecting cable supplied with the speakers would be suitable for that purpose, although if the plug it provides is the 1/4 inch type you would have to get a 1/4 inch to 1/8 inch adapter. That kind of adapter is readily available at Radio Shack and elsewhere.

If for some reason that doesn't give good results, another approach would be to purchase a "speaker to line level converter," and connect it between the speaker outputs of the DAC/Amplifier and the Line In "B" jacks of the main speaker. You can Google that phrase to find those devices, which are generally intended for car audio applications, and are inexpensive. Not sure what kind of sound quality they would provide, though. But hopefully the headphone jack approach will work well, and obtaining one of those devices won't be necessary.

-- Al