WS-6.2

You need a certain size to get low frequency extension. Smaller ones are both limited in that — and quality options outside from RSL are more expensive. See e.g. Kali Audio WS-6.2 (EAC YT review) studio monitor subwoofer. Though, obviously there are lesser quality cheaper small subwoofers out there.

Honestly, with a $300-400 budget, I think you would be better off with either switching to a subwoofer that's easier to integrated with the Kali LP UNF. Or switching to set of speakers that will play nicer with a standard subwoofer. For example, you can sell your SVS 3000 Micro subwoofer and buy the

It provides a much better full frequency range, especially when run through a system that can separate signals (vs crossover, which is still not a bad way to go). It doesn't need to be thumping overkill sub like in a club. I added a Kali Audio WS-6.2 to my already very nice Kali IN-5s and the differ

Pretty much anything SMSL and Topping have on offer from about €280/3100 SEK on amazon.se are solid options, for example: SMSL RAW-MDA1 // Audio Science Review review of the SMSL RAW-MDA1 Topping DX5 II // Audio Science Review review of the Topping DX5 II These have good headphone outputs as well, w