Hi Avian,
Good FM reception is always related to the antenna, its height above ground, its directional characteristics and its "gain". Nor can you compensate for a bad antenna with a tuner of super sensitivity. You likely tried the crummy T-shaped dipole wire antenna that comes with most receivers--adequate (barely) for local FM reception with little rejection of noise off its two reception axes.
Get a couple of those little 300-ohm/75-ohm antenna transformers so you can run a 75-ohm shielded coax cable over to the basement window to a simple dipole "rabbit ears"-type antenna that you can place inside next to the window. It should offer much improved reception. Get the kind with telescoping rods that you can tune (slide them in and out for the best reception of a given station) and rotate the antenna for the clearest signal and best rejection of interference.
You might still have to go to an outdoor antenna. But even a 1/4-wave dipole vertical "whip" (like a car radio antenna) outside the window should make a huge difference.
Regards,
