Preamp with Aleph 5 and Thiels

I have an Pass Aleph 5 amp and Thiel CS1.6 speakers and using an Aduio Research SP9 mk I but with upgraded caps and diodes. This preamp sounded fine in an older system but I was told the impdeence of the Aleph isn't a great match for the SP9 and I find that I would like more warmth, more "tube magic". I know the Thiels don't match well with bright electronics so... do I go for an ALeph P preamp? I am very intrigued by an ARC LS 5 or LS 22. I don't need phono. Any help on what preamp might work in this system?
Please forgive me for working around your initial question, but, as good as the Aleph is, I can't help but wonder if it's the right choice for your Thiels.
Output impedance of SP9 is 250 ohms which is relatively low ...or at least should have no problem driving A5 with an input impedance of 10K.

Output impedance of LS5 is (400 ohms) which is a little higher vs. SP9 though not enough to make a difference in your case.
I don't know about the Aleph/Thiels match, but I had the Aleph P with the Aleph 5 and it was a great combination. I would also consider a used Pass X-1 which is quieter, more neutral and more transparent than the Aleph P, though I never had the X-1 and Aleph 5 together in the same set up.
Thanks for the help. I already assumed that an ALeph P would match with the Aleph 5 but the question now is would the Thiels and the all Pass electronics be a good match anyway. The other question is would an LS-5 or LS-22 (or Aleph P) give me the warmth and dimensional quality I don't feel I am getting from my SP-9.
Aleph 5 has a neutral, detailed sound. Lacking body.
Thiel is also neutral, detailed sound. Would make use of tube or beefy amp to give it a fuller sound.
Personally, I'm not very comfortable with the two combo.
But ymmv.
I sold THIEL's for many years, Threshold Amps then, which were Nelson's first company, I believe.
I really liked using a tube preamp with solid state amps--to give a rounder sound, smoother upper midrange to the solid state of the Threshold.
The Pass is much more refined than the Threshold--but still, IMHO can benefit from a really good tube preamp--depending on one's taste, certainly.
Without checking for a mismatch of impedences, you may consider a cj pre, or a VAC pre with this combination.
Good luck and good listening.
I agree with Unsounds point, it seems you need another amp to drive the Thiels to their best - it is a great amp, but it really is not great at delivering current, a bit like a tube amp, and the Thiels need current and more watts to sound their best, changing preamps is not going to change that.
I agree with Pubul and Unsounds about the match between the A5 (which I currently own) and the Thiels (which I have owned in the psat, but not together and a different model). If the A5 had more power and more current, I think it would be a good match with the Thiels more strident and detailed sound (which is what I like about Thiels - great speakers FWIW).

I am running the A5 wih Gemme speakers, which basically use the same drivers as the Thiels, but a tad more efficient. I also run an ARC preamp (LS16II with the "supertubes").

I would never say the A5 lacks body, just the opposite. And I am coming immediately from SET and before that high power high current Aesthetix/Krell FPB/Wilson W/P5.1. I went SET based on all the SET lovers comments on this site, that lasted about 6-8 months and I grew bored with the SET sound - to me I missed the excitement.

I am still not sure if I find that the A5 is a bit under powered for my speakers, as I am thinking I may want to push the music a little more forward. But a large majority of the time I find I really enjoy the performance of the A5.

So, its a tough call. Do you love the Thiel sound most? If so, replace the amp. Do you want the sound of the A5, replace the speakers. I think (for me) that a more detailed speaker (like the Thiels) go well with the A5. A soft speaker, with a "traditional tubish" sounding preamp plus the A5 would be too underwhelming for my tastes, lacking the excitement I am seeking.