I would consider the Analysis Plus OVal -9 and Oval -I interconnect. thats what i use with my 1.5's and Jolida 1501RC. Most "transparent' cable s i've used. Available for sale too as I am upgrading the Thiels.
I use to own the 1.5's. I cabled them with MIT 330 interconnects and MIT 750 shotgun speaker cables. If you can swing the investment I think you'll be happy. Ultimately I would go with 330 shotgun interconnects to match the speaker cables perfect. I also used an MIT reference digital cable. These cables work great with Thiel speakers. The trick is to find them for at least 50% off retail. They can be had for even less if you play your cards right.
I was using 330 shotguns and auditioned some kimber ss and kcag and with my system it really opened up, more clarity, detail, and transparancy. I am now using kcag and kctg with MIT 750+ S3 with Thiel 3.6's and the result is the best I've had and I've had this system several years. The MIT's fill up the soundstage and give the Thiels a presence and weight I haven't gotton with other cables, the transparancy of the kimbers and 3 diminisionality of the MIT's are a great combination in my system. There are no shortcuts unfortunately, trial and error is the only way to ever really be satisfied.
I'm using MH-750 HE (High Enery) speaker wire to the Thiel 1.5s, MI-330 Series 2 from the pre to the amp, and MI-330 Plus from the CDP to the pre. Total cost for the cable was $490 used. You're also missing half the sound staging capability of the Thiels without Sound Anchors stands ($325 shipped). The results are detail, transparency, and awesome sound stage. I would spring for the higher end 330/750 combos if you can but not at the expense of the stands. You will want a musical CDP. The Cary 303 should be great from what I hear. leo.
No longer have Thiel 3.5s, reference speakers in their day. Did use MIT 330 ICs & speaker cables with them. Still have and use them with older ProAc / Forte' ( Nelson Pass ) system. Very Musical! Can't bring myself to part with this system. MIT cables are great match for Pass Lab , Threhold , Spectral gear. Expensive but if you search this or other sites you can get them. At bargain prices? I have tried Many cables; home brew - AQ, Transparent, Kimber, on & on. Keep coming back to MIT ( the more expensive) ones but they keep doing it for me.
Soundstege, images, frequencies, (Have never found them rolled off) midrange timbre, consistently bring me closer to the real thing. MITs "middle of the road" cables are just that. MIT 330s were a top cable in their day just like Thiel 3.5s .