JBL crossover cards for biamping (courtesy robh3606) plug onto 5235 motherboard, though not without struggle. Even getting the bottom cover off is tough (at least for the anxious Zilchster, after dark). Then, as shown, the cards are retained on captive standoffs, and the connectors are snug. Rugged, so there's little likelihood of damage, it's still a chore swapping them in. Don't plan on doing this routinely. Buy several units cheaply (~$100 on eBay) as needed. Indeed, as described above, these are the standard 18 dB cards loaded with components specific to 4430/35. Card designations "peek" through the front panel.
While in there, dip switches (one of two visible here, red) set LP filter parameters, including options for various (but limited) slopes and frequencies. While "flat" is available, I chose a Q=2 6 dB "bump" at 20 Hz to mimic BX63(A)'s "assist" for B380. I know, I know, it's dangerous to boost low frequency below the box tuning point, which may induce over-excursion of the driver, but I promise to keep the gain modest until capacitors come in to shift this up to the recommended 26 Hz. Do NOT try this when biamping a stock 4430, which is tuned even higher!
On to "critical listening," then....
Originally Posted by Zilch
