You are correct, your power amp's maximum wattage is based on the load impedance it is driving. If you look at the impedance curve of the Salon 2's, it averages around 6 ohms, but that is not a steady state number, it varies with frequency. The amp will be able to produce somewhere between 150 and 300 watts depending on the load impedance.
The disturbing question in your post is, do you have both sets of speakers (the Salons and the Rogers) connected to your amp at the same time?
If so, IMO, you should get a separate amp to drive the Rogers. They make speaker switch boxes to deal with multiple pairs of speakers being driven by the same amp, but they are a compromise.
With a speaker the quality of the Salon 2, you should not compromise the amp driving them.
Ohm's law deals with how resistance adds in series or parallel. Running the Salons and the Rogers at the same time from the same amp could present a low impedance to your amp which is not a good idea for the amp or the speakers.
If your Roger's are around 15 ohms average, an Ohm's law calculator show 6 ohms in parallel with 15 ohms equals about a 4 ohm load to your amp.
Not dangerously low, but not an ideal situation. More important is, the second pair of speakers draws a percentage of power from the amp meaning you aren't getting full power capability to the Salons.