I would put the M71 closer to a TLM103 than a TLM193, which is really rather neutral and may well solve your sibilance issue. I also auditioned a TLM67 and would place it somewhere between the TLM193 and the TLM103, in frequency response, but somehow I didn't enjoy as much as either! Maybe a bit too much emphasis on the mids.
It's ridiculous that there are no TLM193s in the UK! A TLM170 would give you a very good idea of how the 193 would behave (in cardioid mode).