Only if the source LD's have a digital audio track on them. The newer players had those ports because LD's started to come out with Dolby Digital and DTS soundtracks on them. These audio tracks were actually digital, not analog like the rest of the disc. So, in theory, playing the digital audio through your toslink or rf digital output would yield higher quality playback because the soundtrack is already digital.
Yes. Think of it this way - if you were to record a song onto audio-cassette and onto the computer (as a .wav file), you would have much higher fidelity from the computer. Thye cassette takes the analog waveform and saves it in an analog format. The computer takes the analog waveform and saves it in a digital format, but it is still an analog waveform. This is why PCM soundtracks (on laserdisc or CD) are so large - it's the whole signal with no compression. In fact, PCM stands for "Pulse Code Modulation". Pulses (with their rise and fall) versus digital bits.
Analog and digital are two completely different animals. If you capture analog audio onto your computer, no matter how high a sampling rate, it will never be the same quality as it's analog source. When the source is converted to digital using modulation, a sample is taken so many times per second -- much like a video camera captures so many frames per second. The higher the sampling rate, the higher the quality, but it can never be the same as the original. PCM audio files are represented on the computer as waveforms, but it's only a graphical representation of the digital samples. If you look at a compressed mp3 file in the same way, it is still represented as a waveform.