Help needed with analog pre-amp question

Hello Friends,
Hope I am posting this in the correct forum, if not hopefully admin will move.

I have two powered sub woofers connected to the Pre/Power Amp RCA outputs on my Pioneer SX-1250. I used Y-splitters and they seem to be working fine. My question there anything I can do that will allow me to adjust the volume of the subs other than adjusting the receiver's volume or gain on the sub woofer itself? I was thinking of a small amp, but do not know if this is an option.

Thanking you in advance for any advice,
Steve R 
You already have an amp in the subs, so another amplifier should not be used.  You could insert a variable attenuator or passive pre-amp in the cables leading to the subs. 
A Schiit SYS? $49.

Use same outputs as now from the Pioneer to the SYS. Run separate L&R channel interconnects to individual subs from the SYS. Am assuming the subs each have L&R channel line in. Control both subs with one SYS volume control.