Ideas of how to connect a pair of Revel Performa 3's to a Marantz PM 10?


I purchased a Marantz PM 10 Integrated amp due to down sizing recently.  I kept my Paradigm Persona 3F speakers and a Pro-ject 10.1 turntable.  The idea was to just have a nice 2 channel simple system.  That works great, however, I also have a pair of Revel Performa 3's subs that I would like to use with certain types of music.  The problem is the only output is the Recorder Audio Out.  I know this would be a fixed output and therefore would have to adjust the volume and crossover from the subs every time volume on the amp was changed.  Generally, I would not be changing the volume level once listening.  Could this damage the amp or subs?  Is there another way to connect these subs to this amp?  Oh yeah, I am 70 years old and obviously not as sharp as I once was, hence not being thorough has led to this dilemma. 
indylover
Is there another way to connect these subs to this amp?
Use a Speaker-level to Line-level Adapter connect your amp speaker output to the subwoofer RCA line level input.
https://www.crutchfield.com/p_543ADP12/Russound-ADP-1-2-Speaker-level-to-Line-level-Adapter.html?tp=...
Hi imhififan,

That is why I count on these Forums!  I have spent hours researching this topic and never once came across this Adapter.  I really appreciate your taking the time to respond and help me out.
Just to update everyone on the success of the Speaker-level-to-Line-level adapter for an amp with no output for subs.  This worked perfectly and didn't affect the quality of the sound, as far as, what I can hear.  This saved me from selling my 6000.00 subs. A special thanks to imhififan for taking the time to respond with this solution.