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.