this is interesting, so not really impossible 6db on scan-speak D6600 ?
Hi mario, nice to meet you, It's very rare find someone who tried and used 6db on scan-speak tweeter.I have done something similar with a Vifa ring radiator, the effective slope was 12db/oct done with a single cap and an LCR network with values very close to yours. The cap was a 6.8uF, it did work nicely with no issues up to about 80% of my amp power, which delivered about 48W into 4 ohm load. I haven`t tried it higher as it was too loud even for me. I see no reason why it won`t work but you`d need to consider time aligning the two drive units. I did push the ring radiator about 3.4cm backwards to achieve perfect phase coherency as I`m not a big fan of tilting the speaker.