gain setting with remote level control

1.  My sub amp has a button that switches from 100mV-1V to 1V-10V. It says that the first one is typical for RCA installs, but my HU is rated for 5V preouts. I'm thinking it should be switched to the 1-10V.

I have a really good DMM to play with but not a lot of time to try hit and miss methods of setting the gains.

Use your test tone CD and sine wave freqs, and set the gain using both switch positions.  Choose the position that allows for some play in turning the amp gain but results in the lower dial position.  Use several freqs in that amp's target range.  Since you are listening for the clipping, you will not need to brush off your DMM.

Gain setting, as you must know, really IS "hit or miss".  You stop adjusting and call it done when you've attained the best "hit".

2.  Also, both the HU and the sub amp have x-overs,, which to use? I really like to ability to turn the sub off all together from the HU.

With the assumption that comparison of gear quality is apples to apples, use the head unit's xover.  You can always try a switch to the other one if you can't get the sound right (when you have more time, that is.)

3.  also where does the remote gain knob come into play with all this.

See if  the manual gives you any specifics about it, but I would consider the remote knob an attenuator.  Set the gain with the remote unplugged, then turn the knob to max high and plug it in.  If the remote is plugged in while setting gain, keep it at max high position.

I'm no expert on bass remote knobs, though.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

1.  Set gain by ear first, as stated above.

2.  Double check your hearing by using the DMM.

• https://www.the12volt.com/installbay/forum_posts.asp?tid=71427&KW=gains

You can't really measure impedance, so it is best to use the specs on each coil.  If you have the coils series / parallel like this

and each coil is 1 ohm, then you indeed have a 1 ohm impedance.

You can measure DCR and from that conclude a likely impedance.  DCR * 1.3 = impedance.  Your DMM has internal resistance, so be sure to deduct that from the reading of each coil.  Touch the probes together and hold until the reading steadies.  If your DMM reads .5 ohms (for example), that is the internal resistance that is deducted from the coil reading.  (My digital multimeter has a .8 ohm internal resistance.)

Read a coil for DCR, deduct the internal resistance, then multiply by 1.3 to conclude impedance for that coil.  Reading just one coil should suffice but you could read all four and average it if you want.  If you conclude that each coil likely has a higher impedance than 1 ohm, use the parallel and series calculators linked in the left column to find the total impedance presented to the amplifier.  (If wired correctly in series / parallel, the result of one coil will be the same impedance as all four wired coils.  For example, if you conclude that each coil is actually 1.3 ohms, the resulting load on the amp will be 1.3 ohms.)