I am not familiar with that table or how close you keep your laptop to your system, but it may be possible to use the regular audio out from the turntable to the receiver while using the USB out to your laptop so you will not need to use your laptop's headphone jack to listen.
As for improving quality of the audio from the laptop in general, a DAC could be a nice step. It would take digital audio from the USB of the laptop and convert it to a line level analog signal for the receiver. This will bypass the headphone jack which might not be great. (For example, at work, the desk tops have terribly noisy headphone jacks. I use a DAC/Headphone amp to give a significantly better sound quality. In your case, you do not need the headphone amp part, and there are tons of DACs out there ranging from the double digit price to the four or five digit price range).
Lastly, I would ask if you need to convert to mp3? There are other codecs that generally are viewed as better, but then you can get into big debates about number of bits and sample rates and which is better and which is not as good. If it is a case of the you are using a portable media player that requires mp3 that is one thing, but if you are only using your laptop, it should be able to handle FLAC and other more high res codecs (which admittedly take more memory to store as well).
I doubt the program that comes with that laptop can create FLAC files but Audacity is a free software that can has some add-ons that allow it to record FLAC and other lossless codecs.
Additionally, it may not be necessary to buy a new turntable that has a USB out. There are a lot of ADCs (Analog to Digital Converters) that go to USB. I have a Behringer UCA-202 which is about $30. It works well with converting analog to digital, though it does not go as high res as some would like. Moreover, it has an analog out which serves as a DAC which might clean up your laptop's audio output issue too.
Caveat is that your receiver will need a tape out or line out for best results. Failing that, you can probably use the headphone jack of the receiver but then you will not be listening in real time and the audio level will be dependent on the volume knob of the receiver.
I have been rambling quite a bit now, and probably have provided more options that you wanted...