You're correct - in Classical Latin. All 'S's should be unvoiced. There are too many deviations from Classical pronunciation for it to be that version of Latin, and since the pronunciations are inconsistent I'm going with some sort of Modern/Neo/Mediaeval Latin version:)
That's far too proscriptive. There are a number of politeness expressions used to soften imperative sentences, either with or without the explicit object te. These include:
quaeso 'I ask'
amabo 'I shall love'
obsecro 'I implore'
oro 'I beseech'
In Roman comedy quaeso is more predominately used by male characters and amabo by female ones.
A couple of examples from Plautus:
age quaeso mi hercle translege "go on, please, read it through for me, by Hercules" ( Asinaria)
propera, amabo "Be quick, please" (Bacchides)
I swear I heard both voices read this the first time! It made no sense, so I replayed it and it was alright - just one person speaking (oh, and I played it a third time, just to be sure:) . Either I'm having auditory hallucinations (again??:), or there was a glitch in the playback. Just thought I'd mention it in case some other people were experiencing similar. (Betas love any data:)