There is a shared feeling among lute virtuosos to consider the music of Simone Molinaro technically arduous and difficult to play. The same can be said of the many guitar transcriptions of these lute pieces. I wonder if this is the reason why I can not find one guitar transcription of Molinaro in this Forum? That it is technically difficult to play Molinaro may be true for some of his works, but certainly not for all the Fantasias, Gagliardas, Canzonas or Saltarellos. I believe that the degree of difficulty to a large extent depends on the way the process of transcribing the music for guitar is perceived. I like to illustrate this with the Fantasia XIV for lute (published by Molinaro in 1599).
In general one could say that the compilation of the original instrument, together with the selected key, the specific tuning of the strings ( if relevant) and the composition itself forms a unique musical entity. Changing one or more of these elements has serious consequences for any transcription.
When I start transcribing lute music for guitar my approach is as follows:
Step 1: Original key; guitar with original lute tuning.
My starting point is to stay as close as possible to the original. Fantasia XIV is written in tablature. The key is F-sharp minor and the tuning of the lute is similar to that of the guitar with exception of the 3rd string: from g to f-sharp (see facsimile below, showing the first measures of the Fantasia XIIII). The transcription I made of this version (see PDF Fantasia XIV Molinaro fis minor; no fingerings yet) does not feel good. Many spots are arduous. Already the second measure gives technical problems. This option, as I see it, does not fit well for the guitar.
Step 2: Change key; but keep guitar in original lute tuning.
Change to E-minor seems to be best option. The pitch can be easily adjusted with a capo. However, using the lute tuning does not really support the sonority (open strings) and does not improve the playability. By changing the key, the effect of an open f-sharp string has gone.
Step 3: Change key; use standard guitar tuning.
I was surprised how well E-minor together with the standard guitar tuning responded to Fantasia XIV. And for a struggling intermediate as myself it is now relatively easy to play. As if the Fantasia was written for guitar in E with a strong open g for the middle voices!
(Please visit my website beumingguitar.com where you may find more playable guitar transcriptions of Molinaro and other Italian and Netherlandish lute composers of the 16th century)