I own a Pathfinder 15R, and I agree it's great value for the money, still, I couldn't keep myself from performing some mods.
I replaced the original op-amps with 5532s ( and it did help in lowering the noise, are you sure your 5532s are not crappy chinese fakes? ) and added DIP sockets for a quick replacement, but as a matter of fact I did the major mods on the PS and PA sections.
I replaced the original PT with a toroidal PT, with a slightly higher voltage and a better current rating, then I changed the rectifier to a 4 Amp bridge, this allowed me to increase the filter capacitors' value ( to improve the dynamic range ). I also added voltage regulators for the preamp section ( to avoid early clipping on the op-amps due to voltage drops when the amp is driven hard ).
I substituted the output chip - seems to me it was a TDA 2030 - with a TDA2040 and changed the original 8" speaker, putting in a 10" Celestion I salvaged from a wrecked Cambridge 30.
Hope this helps