Also be aware that the JBL and non-JBL systems are completely different. JBL uses MOST interface for audio, and the non-JBL uses analog (non digital) pathway. This will determine which route you go with an aftermarket amp/DSP.
I replace all of my speakers with Morels and insatlled a Audison AF M8.14 DSP amp myself. I have the base audio which makes this much simpler. Your JBL system runs off a MOST interface that will need equipment that utilizes the MOST interface. Either an amp with built in MOST inputs (Mobridge...
I was thinking about taking a shot at one of the Xtrons screens to see if they fit....... I just do not know what model BMW our screens are interchangeable with (if any)...
Can't wait to get this lil fella hooked up. Last part of my audio upgrade. Have Morel hybrids all around with an Audison 8.14 amp/DSP on them. This 12" will get 1200W from an Audison AF M1D.
I believe some here have had success with the Mobridge K2. You will need an amp with MOST input. The JBL system uses MOST fiber to carry audio signals. Search the forum. There are a few good threads about the JBL system DSP upgrade.
My advice would be to get a DSP amp tuned correctly before anything. A DSP tuned properly will dramatically improve the stock system. Then if you would like to take a step further, sub and/or aftermarket mids/tweets. I would put the money you were going to spend on stock Z4 speakers to an actual...
I may be in the minority on this one but I love the look of the exposed filter over the box. I do have this setup and I will say the mushroom filter is noticeably louder than a cone filter on this setup (ran both).