yekke2: “I think the answer to this is R’ Chaim’s vort. R’ Chaim explained that ספק דאורייתא לחומרא only obligates an action that will remove you from the ספק. For example – nobody who davens Nusach Ashkenaz will say Krias Shema in Sefardi or Temani pronunciation, although it is a חיוב דאורייתא and there is certainly a chance that the Temani mesorah is correct. So why doesn’t ספק דאורייתא לחומרא obligate you to say Shema in as many pronunciations as you can? The answer is – since even after you say Shema a second time, you still will not have ודאי been yotze the chiyuv, you are not obligated.”
Besides for which this vort is probably kneged halacha (as mentioned by Tom Dick n Harry) and that its only cited in Rav Chaim name, we have to stop using these Brisker vertelech in halachic arguments. Its important to note, Rav Nissan Telushkin — who was a Talmud of R’ Baruch Baer Leibowitz — wrote in Taharat Mayim (p. 89 see note on the bottom of the page) that Rav Chaim on the Rambam was not intended as a halacha sefer. Brisker are the ones who are messing up the mesorah with all these extracurricular arguments.