Large Room-Rehearsal/Recording/Mixing space, need advice.

I am assisting a band with the acoustics in their rehearsal/recording and mixing space. It is fairly large although the dimensions are slightly unfortunate -L 9.8m- W 10.8m- H 3.3m. I have designed a few rooms but none so large and with such a scope of use. It needs to hit this sweet spot of being usable as a rehearsal space ,recording as well as a mixing room. The band uses in ear monitoring and most likely the amps will be in a separate room. They will be playing drums during rehearsal as well as recording drums in this space , they also have a grand piano so these need to sound nice when recorded. Mostly they go to a proper studio for final recordings but they want to be able to capture moments in there and have the option getting usable recordings. They told me that they spent a lot of time out of the room , in the coffee area as the room just didnt feel inviting or cosy to spend time in. The room is untreated as is except for large superchunks that I advised them to install a few months ago as minimal treatment, since then they have decided to properly treat the room. The superchunks did clean up the low end somewhat , but it obviously needs more work . I also suggested they put up an absorber above the drumkit as well as hanging drapes around the kit to keep the drum noise down a bit for rehearsals, There is also a noticable upper mid range flutter echo in this space at the moment. The front wall has wooden vertical wooden boards , I suspect this was done for aesthetic reasons although it does have rockwool behind that structure. I guess I am looking for some ideas and experiences from you guys , seeing if you have any suggestions before I get started. Here is a quick Sketchup picture. And here is the sketchup file if anyone wants to have closer look. https://www.dropbox.com/s/lnp83yk9nrbf5 ... y.skp?dl=0 I did some measurements before and after the superchunks. These are pre and post superchunks, measured at the mix position. Here is the Mdat file , measurements post Superchunks. https://www.dropbox.com/s/r9fyaspddeaj6 ... .mdat?dl=0 Thanks for your time.

Here is the Room calc graph.

I think I will be aiming for around 400 -550 ms "Rt60". I would be aiming for 250-300 for a control room but the room is multipurpose. This means I need about 135 m^2 of absorption roughly speaking. Having said that , this goal is somewhere between a listening room and a mix room , I might have to go a bit more lively or go for variable acoustics to retain the recording space acoustics. Schroederfrequency is about 62- 70 depending on standard chosen, most rooms I have done have been way higher then that so this is a new experience in that respect. Might be smart to just assume that the Schroederfrequency is around 200. I guess some sort of slat walls might work here. Any thoughts?