That tone should work. It's generally a 40 to 80 Hz "noise" tone. As long as you use the same tone, at the same level, for all the subs, it'll be fine.
If you have 4 identical subs, you want to use a level for *each* sub that results in a *combined* level of 72 to 78 dB when all the subs are placed back in their in-room positions. This will allow the combined subwoofer system to be properly calibrated with the speakers within the range of most receivers and pre/pro's. More below...
In my room, I find that a nearfield setting, (with the mic 2" from the middle of the driver), of 88 dB results in a combined level of 76 dB when each of the subs is placed back in its' in-room position. However, I have 3 dual opposed subs, (6, 15" drivers in 3 cabinets), distributed unevenly around my room. That same 88 dB setting may, or may not, work for you with 4 downfiring subs, and without knowing their in-room placements.
My suggestion for you is to start by having all the subs in their in-room positions, set them all to the same gain setting, and then measure their combined output at the Primary Listening Position, (PLP). If they're higher than 78 dB, lower them all the same amount until the combined SPL reads 72 - 78 dB. If they're lower than 78 dB, raise them all the same amount until the combined SPL reads 72 - 78 dB. If they are all set to the same gain setting, and you're confident that the identical gain setting results in them being gain-matched, you're done. However, some subs will have variations in the gain at identical gain settings on the amps. In that case, if you want to be more precise about it, you can proceed to the next step.
Start by moving one sub to the middle of the room. Lay it on its' side and place the mic/SPL meter 2" from the driver. Play the subwoofer test tone and measure the SPL. Mark the exact location of that sub on the floor with masking or painters tape. Without moving the mic, move that sub out and the next sub into the exact same position and adjust the gain until it reads the same SPL as the 1st sub. Then repeat that process with the other 2 subs. Then move each sub back into it's in-room position and measure the combined output at the PLP. It should be within the 72-78 dB range. If not, adjust each sub by the exact same
amount until their combined response is within that range.
From that point, you can continue with your Audyssey XT calibration. It's not terribly important to have a -5 to -8 trim setting in the receiver after running Audyssey, but I personally prefer it. It allows for the ability to add some input signal to the subs to run the system a little "hot" without exceeding the "0" trim setting. Some sub amps can be overdriven with an excessively high input signal. Staying below "0" ensures you won't overdrive the input of virtually any subwoofer amp.
However, you may not be done yet. With 4 subs, if they end up being different physical distances from the PLP, you most likely need to do the Audyssey subwoofer "Distance" tweak, as written by Keith Barnes here: