Interesting timing on this user's experience with low sensitivity speakers - I'm going through something similar the last day or so.
My secondary speakers are a set of Harbeth P3ESRs, which I listen to every once in a while. With my main amp (a Karan KA-I180 Mk 2), I could never really get along with the Harbeth's. You would imagine an amp like that could make anything sound good. All the audiophile boxes would be ticked off when using the Karan/P3 combo - clarity, texture, imaging, etc., but I just couldn't get emotionally involved in the music. I always wanted to just take the P3s out.
Enter the Spark. I've had the Spark for a while and was using it happily in my office system, which ended up being dismantled, leaving the Spark idle. Completely on a whim, I decided to try the Spark with the P3s and damn - it's way more enjoyable to listen to than the Karan/P3 combo! I'm sure all the audiophile stuff is better represented by the Karan, but there's absolutely no doubt in my mind that the Spark/P3 combo communicates the emotion in a performance WAY better. I feel like I've finally understood and gotten the measure of the P3s in my system for the first time. I'm literally listening to this combo right now and feeling like I need to check out Harbeth's more expensive offerings.
Sometimes unexpected pairings yield better results. Definitely the case with the Spark and P3s. Kudos to Boris on the Spark. The fact such an unassuming, inexpensive amp can run comfortably with much more expensive, inefficient speakers should open people's minds to the possibilities in "unconventional" pairings.