Hi ,
I also bought Heco victa Prime 252A Subwoofer. Bought it from Germany 298 Euro.
Set it up with Yamaha RXV 350 5.1 receiver (12 year old but in perfect condition). Nice sub and it is going as low as 21 HZ when I played a test file, and yes I can hear clearly. I have not much experience with multiple subs, till now I was using a Yamaha sub came with NS P100 speaker set. Now I have upgraded the system with Dali Zensor 3 speakers for front.
I think this Heco sub will take some more time to fully break-in, however I am very very happy with the sound. The bass is tight and I find it better than Polk psw 110, which I listened at my friends place.