Mark Levinson or Pass Labs...What is each's "House Sound" like?

Check out the thread on Audiogon titled  "My Long List of Amplifiers and My Personal Review of Each!".  The OP reviews dozens of amps including the two brands you are asking about.  It's a long read but well worth it.  You can also ask him any questions you might have regarding just about any amp you can think of.  He reviews mostly solid state amps....Hope this helps.

I owned an LS7 once and didn’t keep it very long. It’s was ARC’s entry preamp at the time and I felt the SS LS3 was a much better preamp. My first thought reading your post is I’d look at your preamp first. 

As as far as Levinson or Pass on your Thiel’s, I’d go Pass. A Pass is going to be smoother on the top where an older Levinson might have a little bit of an edge on your speakers. My opinion a Pass will be a safer choice if you can’t listen first. 

I have not had the pleasure of listening to an ARC D240 MKII, but I once owned a 100.2 which I greatly enjoyed. If your amp is even close to a 100.2 I’d really look at your LS7 first. I should have kept that 100.2.