Question is will the somewhat high output impedance of the amp still affect the bass negatively?Probably not, unless slightly enhanced bass is seen as a negative. It won't be by much though.
Overall impedance showing in my multi-meter is 4.1 ohm.That is the DC resistance and is only the drivers that don't have a cap in series with them. To really know the **impedance** (as opposed to resistance), you need a different test, since impedance often relates to frequency and can be quite different from resistance!
You'll need a variable resistor that might cover the range of the drivers. A 50 or 100 ohm potentiometer should do the trick. You'll also need a sine wave generator which will drive the speakers. We're not talking about any power here. You might be able to find an app for your phone that will do the job. You'll also need your DVM.
Set the frequency at which you want to measure. Put the potentiometer in series with the speaker. You'll only be using the center connection and one side. Apply the signal. set the control so that the AC voltage drop across the speaker is the same as the control. Switch to Ohms and measure the control (out of circuit is best). That is the impedance of the speaker at that frequency. Continue to do this for all frequencies of interest.
You'll see that there is a low frequency impedance peak, followed by a lower impedance which then rises as frequency is increased. There might be dips at crossover frequencies. Check the areas of interest (crossover frequencies and then 500Hz above and below each crossover frequency). Then you can draw this all out and see what you got.
As a general rule of thumb when you put drivers in series they really should be the same kind of driver for the reasons Al points out above!