Best Tubed Preamp For A Warm, Rich Sound, Yet Still Detailed and Agile

I'm not really sure what you are looking for. From what you have posted, it sounds like your preferences are toward the rich and warm sound, though you would like a bit of detail. 

You have to understand that as you get warmer, richer, sweeter sound, you also lose detail and definition. The higher the resolution and detail, the less warm and rich sounding. So obviously you cannot go in two opposite directions at one time.

That said, if I am reading you right, the Cary SLP-05 or a Joule Electra LA-300ME may be just what you are looking for.  
The Allnic L-3000 mk 2 is more similar to my original suggestion of the VAC Renaissance mk III. These are not the warmest or richest sounding tube amps. The VAC and Allnic both lean more toward the resolution/detail side of the fence, but with a bit more warmth than the likes of ARC.

It seems like you want more warmth and richness, so Cary, CJ or JE may be what works best for you.

What amplifier will you be using?

There have been many worthy suggestions, but as Georgehifi alluded to earlier impedance compatibility with the amplifier needs to be considered. Also, compatibility with the amplifier in terms of gain, and with respect to whether both components would be best suited for the same type of interconnection (i.e., balanced or unbalanced).

Regards,
-- Al

Here's a few you may want to adition. VTL 2.5, Aesthetix Calipso, Wyetech Pearl, Lamm LL2.1, Sutherland N1. (I know the N1 is solid state, but I'm still recommending it)

The amplifier that I will be using the preamp with is superb, but not well known, which is why I failed to mention it earlier. It is the Wells Audio Innamorata, which is single ended with an amplifier input impedance of 50k ohms. 

JMC Grogan2, I completely understand your point. I'm trying to find the sweet spot between warmth and richness, without sacrificing too much detail and speed. I particularily appreciate your thoughts as you and I share, I think, somewhat similar tastes. I hope your Rowland Model 6's are still serving you well!