Using TIU as control only...not power distribution

yes it can. Search for connecting TIU in "passive wiring" mode. You may need to add a filter?

@gibson man posted:

I plan on running a large loop...using a lionel tpc 300 with two 135 watt bricks to keep the wattage/voltage up over this long run.  Are you using TMCC/Cab1 or Legacy/Cab2?

I'm using this power setup for more power plus the added circuit breaker protection built in.  What added circuit protection?  Neither the TPC nor PH135 have very good protection.  Are you adding additional fuse/CB and TVS protection?  If using Legacy, go with the 360 Legacy PowerMaster.

I will be running both DCS and Legacy/TMCC engines.

Can the MTH tiu be connected in the same manner as the legacy command base...as a control unit and not a power control...while power is applied to the track through a separate source?  Yes.  See diagram below.

If so...how should it be connected to the powered track?  There is a 22uH filter because the circuit protection is a PSX, which does effect the DCS signal a bit.  The filter may not be needed if you use a different type CB.  The TIU needs to be powered by a separate source, like a Z-500 or Z-750.