The penultimate MiniDisc recorder worth its salt, centered around the ATRAC algorithm in its ultimate original verion (4.5) and the 20bit Wide BitStream.
It was built like a true ES unit and was an excellent recorder costing 180,000¥ and weighing 14,3kg - as costly as any X7 CD player !
The Frame & Beam structure was here aided by BASC, mixing brass, aluminium and steel for even lower cabinet resonances.
Two R-Core transformers feed everybody happy while the famed VC filter (not yet VC24) allows for four different LPF shapes.
Digital output can be selected as 20bit (normal) or upped to 24bit.
It just is a pity the MiniDisc format itself started out so unausipcuously with the original ATRAC (3.0) which was... well... it really stunk.
That is, pehaps, probably, people weren't used to crappy MP3s yet.
24bit d/a excepted, the MDS-JA50ES can be seen as the best possible iteration of MiniDisc.
Yet to come was the upgraded MDS-JA555ES, ATRAC Type R and the ultimate Type S before said format was relegated to portables and unsuccessful upgrades (market-wise) like the Hi-MD or the earlier Data-Discman.
A fair review of the JA50ES is here, and a detailed description lies here.