what has a Thiel soundstage, but more sensitivity?

Your Thiel CS0.5 are 87db sensitivity / 4ohm nominal (3.2ohm min)impedance and are fine with your 60 wpc Pass Aleph 5 but probably challenge the amps on dynamic peaks a tad. If you like Thiel, then you can try the CS1.6 (entry level floor stander), which is a 90db sensitivity speaker with similar impedance characterisitics to the CS0.5. It should be more easy to drive than your CS0.5. They are in the $2600 range new here in the US but don't know pricing in Europe. The other suggestion is JM Focal 1007Be monitor speakers which is an 89db/8ohm nominal (3.2ohm min) speaker. Should be much easier to drive given the more forgiving impedance rating. Highly resolving like the Thiel and soundstages/images very nicely. More pricey than the Thiel CS1.6 but you may be able to get them within your budget used. Good luck.

Triangle speakers perhaps?

I only have small Triangle monitors but they are most resolving and transparent and I run them effectively in a typical modern family room off a 20w/ch vintage yamaha receiver (with a separate powered sub).

I've heard Focal Profiles also and those have a lot of the same strengths as well.

Dunlavy.

I scrapped my 1.2's in favor of Coincidents. Very similar sound and much easier to drive.

maybe some of the Meadowlark speakers?? they have been out of business for several years and their speakers are available at great prices used. they are time co-herent designs ala Thiel but easier to drive.