Salamun Alaikum.
I agree with the sentiments. The Quran is absolutely clear. Congregational prayers aside, in my personal prayers, I endeavour to keep my tone slightly audible in line with the verses.
However, the only possible rebuttal I can perceive argued from the Quran alone, is that this is a reference to the previous followers of scriptures (17:107-109) where the Prophet is advising them.
This would be a fanciful assertion in my personal opinion as it would be difficult to accept the Prophet instructing the followers of the previous scriptures how to pray and then have differing methods for his own people.
I don't think the verse could be any clearer as to which tone to use during prayer.
Regards,
Joseph.