Outdoor FM Antennas Used Indoors (Urban)

I live in midtown Manhattan in a high rise building and have a significant multipath interference problem. I have just bought a Marantz 10B tuner and need help weighing my options with regard to outdoor antennas used indoors. I have read the literature of Magnum Dynalab and Fanfare regarding their ST-2 and FM-2G antennas respectively. The two antennas seem similar if not completely identical. They both are omnidirectional and both claim to significantly reduce multipath distortion. This seems to be an impossibility to me, that an omnidirectional antenna can significantly reduce multipath interference. So, what I am asking is if someone living in an area similar to mine (in a steel reinforced concreate building with lots of nearby tall buildings) can actually vouch for either or both of these antennas as having significantly reduced multipath distortion particularly when either or both of these antennas are used indoors. I have read all the recent Audiogon threads on FM reception. Some suggest the use of the Magnum Dynalab Signal Sleuth. I'd like to avoid major additional expense and extra "boxes" if possible. I have tried the Terk powered antennas, the BIC beam box etc. with other tuners I have owned and while better than the FM "T" antennas, I am looking for something better. Don't want to go the "cable" route either unless I get desperate. I'd just like to get the performance that the 10B is capable of. Let me know if either or both the MD ST-2 or Fanfare FM-2G can do the job alone. Any comments about what improvements were offered on top of these antennas by the Signal Sleuth would be appreciated. Thanks in advance for all your good advice!