The ATR series uses Teac's Omega tape path geometry (basically with the tape loaded the path looks like an upside-down omega)...I'll have to refresh my memory but it was purposeful in reducing flutter and improving handling and tape to head contact...designed for heavy-duty shuttling in a video sync environment...notice that the pinch roller is on top of the capstan and serves as the impedance roller so tape passes through less components. This design was first seen on the 58 1/2 inch 8-track and was carried on to the MS-16...that's the ATR series' lineage...the 58 was marketed as Tascam's first recorder/reproducer for the professional market and was their first with balanced +4 I/O...if Ghost is right that the ATR series uses the same amp cards as the MS-16 that's interesting as the MS-16 uses the same amp cards as the 58...neat-o...when you put pics up can you capture one of an amp card and if you got the manual would you be willing to link a schematic scan?
If they are the same cards then they may not properly bias high output tape like SM900, GP9, 499 or ATR tape...the MS-16 and 58 bias amp is limited by the amp card circuitry but this may have been changed on the ATR series...I would be surprised if they hadn't. I could tell if I had a schemo for your amp card. None of this means you can't run super high output tape, but if the bias amp circuit is the same as the MS-16 and 58 it won't properly bias the tape. There is a simple mod though that will allow stronger bias current on the MS-16 and 58 and AFAIK it is safe...Jim Williams has done it and evm1024 on this forum has done it as we'll. I'll dig up the thread or he may chime in.
Anyway, really nice systems. Congrats.
What else is in your stable?