So what do you think will happen?

I'm not sure I understand exactly what Liberty is doing with this spinoff, but it appears that LSXMK (and LSXMA and LSXMB) will convert to some number of SIRI shares (originally 8.4 shares, but the latest filing says "conversion ratio to be determined on Sep 5"), then it seems that SIRI will do a 1:10 reverse split (that's new to me, but if I understand it correctly, that's what they plan to do on Sep 9 when the spinoff officially happens).

I don't own any LSXM*, but I do own some SIRI. I sold all of my SIRI last summer when that sudden spike to 7-something happened on a short squeeze (July 20, 2023). I remember that I had just exited my physical therapy session and casually glanced at my quotes tab on the CNBC app and was shocked and thought it was some sort of mistake. But I sat in the car, and opened the brokerage app (that I usually use only a few times a year, I prefer using a big screen for brokerage stuff), and I made a snap decision (which I almost never do), and clicked the box for "sell all shares" and the selector for "market order", and I got executions between $7.50 and $7.53, not exactly the max for the day, but still 7-something as it began settling down from the short squeeze. Later I bought some back in the 3's and then 2's because I was lending the shares out at absurdly high interest rates, like 20% to 100+% rates. Even last week, the rate I was being paid for lending those shares was in the 80s or 90s! Nothing like big demand from people shorting a stock you own. That gravy train will end on Sep 9th, and I will probably sell the shares any day now.