I have resuscitated several hundred hours-worth of 0.25-in open-reel 15ips and 30ips tapes up to 30 years old for broadcast, not only by using external USB connected sound cards, but by using the whole rigmarole:
1) 'baking' tapes at 50°C for several hours to encourage the magnetic material to stay attached to the tape;
2) holding a cotton bud wetted with isopropyl alcohol to the business-side of the tape before the read head throughout the whole playback, to overcome squeal, sticking and shedding of the magnetic coating;
3) recording to beta video through a PCM, or straight to DAT, so as to be able to eliminate stop-starts in the analogue sound capture;
4) digitizing through an ESI U2A sound-card directly.
It helps greatly if the analogue tapes were properly set up for level (0dB) with several tones from 500Hz to 10kHz or so, but this is not alterable if it wasn't done in the first place, or unless you have a good and experienced ear. Commercial LPs, unless extremely worn, should need only de-correction of RIAA emphasis. It also helps if you have an analogue mixer in the path for frequency and level correction before digitizing. None of this may be of concern to you, and be assured that a good wave editor in your Mac can be invaluable for some corrections: filtering, normalizing, even various FX if that is your aim, and especially to remove a few adventitious pops or clicks, but vile quality analogue sound in can rarely be turned into more than even-more-vile digitally recorded sound. A wave editor can often be used to hand-redraw as little as 0.0001sec sections of waveform, but this has limited value in a piece of music from 3min to 1hr long. There is no substitute for the best quality analogue input that you can arrange, or care to arrange.
Dear as I hold many of my LPs dating back to the mono era of the 50s, I still only remaster them to CD when I am convinced that there will never be a commercially-remastered reissue. Life is too short to do otherwise.
Apple IIe; 68K: 20DT/T + 5PB; PPC: 9DT/MT + 3PB + PTPro; G3: 7DT/MT; G4: 3T