Depends on several factors.
Does TRS19 support SLI, no it doesn't, neither does TANE.
Does SLI work with it, unknown, it may have worked with TS12 an TANE, jury is out on that.
Done some research, for some Games 2 x 1070TIs in SLI seriously out perform a GTX1080TI, for other games it's no better or worse or doesn't even work.
Need an uprated PSU for 2 x 1070TI's 650 watt preferably higher and good quality, not cheap for Gold Rated and a high bandwidth SLI Bridge ($50) for anything over 1920 x 1080 adding to the cost.
May need to beef up case cooling as the lower card will heat up the card above it.
Use of SLI seems to be falling off unless you are into extreme benchmarking.
GTX1080TI still seems to be the card to go for performance and value for money rather than the grossly overpriced currently rapidly dying RTX20XX cards.