From: Piotr Gasiorowski

[...] /ɧ/, /ʂ/, and /ç/.

The last one is pretty straightforward and exhibits only little variation (affricate [cç] in some areas). Phonetically, it's not a German [ç] as in 'ich', but rather a sound intermediate between [ç] and [ʃ], something like [ʃʲ] (or [ʧʲ]), pretty close to (a shortened) Russian <щ>. 

From your description, it looks like [ɕ] (= Polish ś, which is precisely halfway between, say, German [ç] and English [ʃ] = Chinese x, Japanese sh, etc.), the so-called alveolopalatal fricative. Your "retroflex" must also be pretty close to what I prefer to transcribe as [ʂ] for Polish sz (against the traditional but inaccurate "[ʃ]" typically found in hadbooks of Polish phonetics).
Yes, I think [ɕ] might do the job for the Swedish sound as well.
(By the way, the historical sources for this sound are tj, kj, and k before front vowels.)

Much of this is beautifully parallel to various Indic stuff, isn't it?

A nice thing with the Swedish retroflexes is that they are part of what might be described as a completed sound change that is given prolonged life through sandhi: Ser du'n? (Standard Swedish Ser du honom?) 'Do you see him?' [seːɖɵn], Det tar tid 'It takes time' [detαːʈiːd], etc. -- also kind of a parallel (cf. Old Indic e, o /_C ~ ay, av /_V).