I also have the Perlisten D12s. It has evolved into a very nice sub.
Initially it needed lots of break in as I couldn’t get enough gain out of it. But now is performing well. That driver when new is really tight and seemed quite closed in. It wouldn’t keep up with the Altec 604 due to the high efficiency of the speaker.
With the D12s hooked to the preamp, the Altec would be fairly loud at 9:00 on volume, but the Perlisten sub even set to the highest gain was not loud enough.
Over time the sub seemed to loosen up and I have been able to turn the gain down to 9.5 or 10 (out of 12)