Twenty years later, we are unfortunately not much further forward! I was contacted by a Hungarian some time ago, who was researching the Insurrection and wanted to know the source of the quote from Charles about the Primatial and Neutra Insurrection Hussars being useless. He might have found something, but I haven't heard as yet.
The Primatial Hussars were a unit of volunteers raised and financed by Archduke Carl Ambrosius, Archbishop Primate of Hungary, whose base was in Gran (now Esterzgom), which is on the southern bank of the Danube close to where it turns south towards Budapest. As such it is "Below the Danube, but this was a volunteer unit with troops from probably both sides of the Danube in western Hungary (including Slovakia as now). They should not be confused with 12th Palatinal Hussars, a regular unit formed in 1800 from Insurrection cavalry from the Jagyzier and Kumanier peoples of central and eastern Hungary and whose Inhaber was the Archduke Palatine (viceroy) Joseph.
Although Eder shows them in nice uniforms in 1809, http://www.uniformen.napoleon-online.de/picture.php?/39/category/10
this was the regulation, not the reality, which was that the Insurrection was at the back of the queue for money and kit. The regulations had themselves changed the mixtures of uniforms of 1797 and 1805 into a single dark blue uniform with white lace and the four colours of shako from the four districts. However, the earlier units in these areas tend by about 3-2 to be in light blue uniforms with mostly black shakos with a variety of cord colours - black, yellow, black-yellow and red, with white and yellow buttons. The 1797 Gran uniform is light blue with a light blue shako and yellow buttons & cords. However, it is not far from Budapest, which is dark blue with a black shako and yellow-black cords. Given the regulations and the production of shakos for the infantry (which were originally simple peaked tubes like the existing Hussar shakos), the likeliest uniform would probably be dark blue with a black shako and white lace with shako cords in yellow-black as per the regulars. A key difference would be the raw (or red) leatherwork.
That said, in "Das Buch der Husaren" (1999) by G Sagvari, who was the hussar expert at the Hungarian Army Museum at the time, there is some new artwork, which shopws elements of the 1809 uniform. It was obviously an attempt to standardise the Insurrection's kit (although 1809 would be its last call out) and in particular, it features F1 sabretashes in place of the district emblems on earlier figures. It shows a detail of the dolman and pelisse. The dolman is light blue with cords, but no buttons, except to do it up, and most interestingly, a red collar and red pointed cuffs edged in yellow, whereas the regulars just had some cord decoration on the cuffs, which were the same colour as the rest of the dolman. This is interesting,in that it was the sign of volunteer infantry units like the EK legion that the pointed red cuff signified their volunteer status as units prepared to fight in the field army. Likewise, the pelisse is somewhat simpler - it only has a ring of fur on the cuff and there are only four lines of lace, again with only the one line of buttons. They say these are Insurrection uniforms, but it is possible that the Primatial copied the regs directly at the Archbishop's cost, while the Insurrection in truth was probably more like the earlier multi-coloured units.
So, that is all that can be said at the moment.