Forgive the possibly stupid question, but are you
really sure that your Tosh telly can't accept RGB?
I use a 2939DB, which from your description (i.e. 7 years old) is older than your own TV and this set accepts RGB via 'SCART/AV 1', with AV/s-video on 'SCART/AV 2' and s-video on 'AV 3' (using a front or rear s-video socket).
From my own experience, the alternative s-video (as you appear to be using composite at present) is most certainly a 'better way' - provided reasonable cabling is used, that is

I use very cheap cables (by
anyone's standards!), but the worst of them certainly exhibit 'faults' in a big way - with colour bleed being the worst artifact. In short, I can recommend s-video as an upgrade to the basic composite picture.
I do also wonder if you are in fact using RGB? I am not questioning you directly; but your words once again echo the sentiment of others regarding Tosh TVs and RGB. More specifically, the RGB picture has often been described as 'muted' - or words to that effect!
It is only during the last year that I have experienced prolonged use of alternate sources via my TV and I can say that things appear to depend on each component. Yeah, I know... 'Durrrr'!

What I am trying to say is that in my experience, there doesn't seem to be an appropriate 'catch all' summation regarding any one form of input/output - it very much depends on the output of the source, the cable used... etc. What I have seen is that (on my TV) RGB gives a duller, but wonderfully sharp image and natural colours. Composite gives the leased focus image of all and one lacking in detail, but gives a boldness to the image that is missing with RGB (although this can be compensated for via judicious use of the brightness and contrast functions

). S-video is the 'half-way house', returning detail (relative to composite) and contrast (relative to RGB), with a reasonably pleasing picture (depending on the source and cabling used).
Re: use of a receiver, as far as I know, it is merely a matter of convenience - with the receiver acting as nothing but a 'pass-through'. Aside from potentially using fewer remote controls and button presses, I don't believe there is any advantage to using the Pioneer for video.
I hope at least some of that proves useful, though I expect someone better informed will give the advice and help that you need. Good luck, anyway.