I’ve noticed some of the 
+ workouts are only available in SLOPE or MIXED mode.
Since day 1 with Xert I’ve grown accustomed to and prefer 100% ERG (Auto) mode which means I avoid the above workouts which limits which workouts I have available to me.
Is it possible to have a MIXED/ERG mode.
I’m talking about workouts such as Test Your Might, Break on Through, VIRTUAL - Ellis etc.
Thanks!
In general, we don’t publish breakthrough workouts using erg mode and the “virtual” series are meant to mimic real courses so are slope mode.
Having said that, you can export them and reimport them to convert them to erg and have them in your own Personal workout library.
MIXEDMODE is another unique feature of SMART workouts.
MIXEDMODE ensures you can tackle high targets when the goal is peak strain not exact watts.
MIXEDMODE also avoids the spiral-of-death wall common with many smart trainers during abrupt transitions from low to high watts.
AUTO mode in Xert players will switch to Slope mode so you can select gears/cadence appropriate for upcoming peak strain intervals.
This is also useful when your ability to attain targets declines due to fatigue and MPA drawdown.
In Slope mode you can’t really fail intervals as long as you try to attain the target. Just like a similar workout outdoors. The last couple sprint efforts in a series may be a bust but at least you tried. 
As an example, read the description of this workout – Adventures of a Lifetime
With this workout you can freely exceed the target watts and potentially prove a change in your PP. You can’t do that if the trainer is under ERG control.
This is also why BT workouts in the library are designed to be ridden in Slope mode. The goal isn’t so much to attain specific targets, but to measure your performance during a maximum effort under fatigue to failure.
Also see this post –
New SMART Workout(s) - #3 by ManofSteele