There are several in this chain who have pointed you in the direction of Cary's SLP-05 ..... well, I'm hear to tell you they are right.
I'm curious as to if all the folks recommending the Cary SLP-05 have read this comment from the OP:
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.
I'm not sure that the SLP-05 is any better than the SLP-98 if you can not run it in balanced mode.
Not to mention the point that Al (almarg) pointed out regarding the SLP-05's output impedance:
While the description of the Innamorata at the Wells Audio website as well as in various reviews indicate its input impedance as 50K, its manual indicates 30K. I don’t know which number is correct, of course, but 30K would be somewhat marginal (or worse) for use with several of the preamps that have been suggested. For example, Stereophile measured the 20 Hz output impedance of the Lamm LL2 at 3.3K, and the 20 Hz output impedance of the Cary SLP-05 at 3.4K, both of which would be just barely acceptable in conjunction with a 30K load, IMO.