And it trains your technic much more. The instrument is more heavy than a normal 6-string classical guitar.
Doing lute, piano or cello transciptions is easier on 8-string classical guitar because you have more strings more range of sound. You can tune it on many ways. I tune it as normal guitar tuning (E-A-D-G-B-E) plus A (bass) underneath and another A at the top. Others normally tune it as a lute or a normal classical guitar plus two more bass strings.
This is not my 8-string guitar but I have exactly the same type - I got this picture from Romanek's website.
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