i've never actually had to print from solaris to an HP printer ... except to say that i use solaris as print servers for windows PC's ...
i have had trouble getting HP's to print if the "File Contents" is not "ANY" ... and i've had trouble with Eltron Label printers because they use 0x000 characters, which the PostScript driver trims off for me ...
however i can't test it on our system because i seem to be missing the HP model from any of our Solaris machines ... i usually cheat and tell them they're postscript because the Solaris boxes don't print ...
You may need to look into alternatives though ...
almost everything i've found on the subject says use Ghostscript to convert PS documents to PCL ... but when we tried this on one of our machines it was printing really slowly (about 1 page/4 mins, and unfortunately no, i haven't got that the wrong way around)
umm ... you can get hold of a Postscript card for the HP4P ... we have one at this site ... but it does come in at $200 (from a quick search ...
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alternatively you can get a new Postscript printer ... Lexmarks are good, and relatively cheap we use the Lexmark E322 (swift machine, faster than our HP6MP)... and it is possible to buy a colour inkjet from HP ... the HP 1220/PS (note the extension) does A3 colour at around $450 ...
hmm ...