First, it should be noted that the "soli", especially in the case of bowed instruments, induce a form of composition aside, it would be impossible for me to explain (think the suites or cello sonatas and partitas of Bach violin or violin sonatas Khandoshkin, etc.), other than invoking great expressiveness. The partition must demonstrate a mastery of the specificities of the instrument by the development of several voices on an instrument used more for melody, for example.
Inspired by Bach, Reger refers formally to Renaissance dances (Gavotte, Gigue) and offers a fugal movement in his first sonata. We feel that Reger has mastered the technical, expressive and harmonic instrument. The music has the depth expected of this type of composition, and listening is extremely pleasant. Really, there is in the work of Reger pearls of impressive purity, as under the patronage of Bach, which, if it is not matched, here is the subject of a tribute which he n would not have to blush. My only slight disappointment comes from the variations of the last movement of the Sonata No. 3.
The interpretation is in good order. Guido Schiefen has excellent intonation and knows how to make his very expressive cello sounds. But I reproach him a tendency to take liberties with the rhythm in too large proportions. No doubt it is in the presence of a romantic inspiration of interpretation, with its share of rubato, but it seems quite inappropriate for cello solos inspired by Bach and consist of dances from the Renaissance. If we are not in the presence of a flawless interpretation, it is clear that the musician is doing with honors. Anyway, the lack of available records makes any comparison difficult.
In short, a successful drive for works that deserve to be better known.