To be fair, as posed your question is difficult to answer meaningfully. What kind of music do you like to listen to, at what volumes and in what size of a room? Are you listening in one position or moving around? Can you describe what kind of sound you like? Without more information, the best anyone could do is look at the specifications for the equipment in question to see if there are any glaring mismatches, especially with regards to impedance and power. There are lots of charts online showing frequency response, impedance (I didn't see any in a quick search but I'm sure they exist), off axis response, etc.
Both speakers are 8 ohms, a good load for this receiver. I don't have their respective impedance curves to spot any weirdness, but I would think it unlikely for mass market bookshelf speakers to have crazy impedance dips that could stress a power supply.
The Pioneers are 92.5dB efficient with 50W power handling; the JBL are 89dB with 250W power handling. So they are fairly close in output. The Marantz will be able to get more volume from the HPM-100s because it doesn't have the juice to push the JBL to their limits.
I have heard the Marantz 2265b and many of its brethren. I grew up with a 2252B but many years later found I preferred the 2270 for it's more euphonic sound.
I have heard neither speaker, so can't comment on their respective sound signatures and how those might or might not jibe with the Marantz. But they are both very well known. The Pioneer was designed by Bart Locanthi, I believe, and was very well received. The JBL is from a line with a tremendous pedigree, culminating in the 250ti, which I think is an "audiophile" speaker by today's standards.
I will however, echo something a previous poster noted, which is that if your receiver is all original, it will definitely not be sounding up its potential. Electronic components age and, if you love this receiver, investing in an overhaul will keep it running nicely for decades to come.