Some things,electrical included don't lend themselves to u-tube and other diy projects. Stated another way "it little knowledge is worse than none at all".
Withthat in mind,I will supply the nessary info you request then it's up to you to do it to code or at least make it safe.
!st determine from the rating plate on unit and strips inside what minium & max amp service is required. The unit can have no strips,1 strip or several strips from the factory. It is not at all uncommon for a unit meant to be used in cold climate to be installed in a mild climate not requiring all the strips. The installer can disconnect 1 or more strips and make a note next to rating plate.
The breaker at main box should fall within max/min ampacity. The wire from main to unit must be equal to or greater ampacity than breaker. The breakers you refer to that came with the unit should equal or exceed ampacity of wire and/or breaker in main box. Breakers must be desighned or altered so when one trips,both trip.
If you have questions about any of that,I'm at your service. If you have questions about how to install it,i can't help you.

Unit is a Trane 5 ton heat pump, air handler TWE065E13FBO with BAYHTR1419 strip(s) factory installed (per label on the unit itself). Long story short I am concerned that the Trane dealer that originally installed it should have either run a second feed from the breaker panel or should have upsized the 8-3 nm. Easy to see that this is the original wiring from when the home was built based on the wall texture/paint overspray on the wiring at the top of the main panel. 8/2 coming off a 60A breaker feeding the outside unit (XL1800 weathertron) and 8/3 feeding both breakers/disconnects (2 60A Square D breakers) in the air handler from a 100A breaker in the main panel. Assuming that the heat strip(s) are wired in a way where #8 is adequate(if wired in at all) its still over protected at the main panel and in my opinion needs to be addressed. Not mentioned when the home inspection was done and not mentioned when a Trane dealer tech from a company other than the original dealer replaced the tstat a few years ago due to the back lighting failing on the original. Old thermostat had emergency heat option not sure this one does (Trane Tcon something which I believe is a Honeywell with Trane name on it). If a second feed was added is there a requirement that the breakers be tied together in the main panel? Trane documentation just says should be wired in accordance with NEC and state/local regulations.

J

Below is what Southwire says about SE. The key pharse " where permitted" indicates it's safe for your aplication but local code has the last word.
"Southwire Type SE, service entrance cable is used to convey power from the service drop to the meter base and from the meter base to the distribution panelboard; however, it may be used in all applications where Type SE cable is permitted. SE may be used in wet or dry above ground locations at temperatures not to exceed 90ð C. The voltage rating is 600 volts. "
You are supplying a lot of unnessary info regarding t-stat and sounds like you arn't sure the strips are even functional. Either way the 60amp and 100amp breakers feeding #8 wire are both too large and should be replaced with 40amp.
I'm not certain I follow what you are refering to when you say"secound feed". If you are asking about laying another pair of wires alongside the existing #8,I am not aware of any way of doing it that meets code. Forgive me if I come accross wrong but I want to keep everone safe. What you are saying is either going over my head or you are getting in over yours.

This may help :
http://hvac-talk.com/vbb/showthread.php?554662-How-to-wire-an-air-handler

Mine has two 60A breakers instead of a 60 and 30 and is supposed to have the single feed kit installed although I have not removed the cover myself to confirm. Per another HVAC forum the answer is that 2 sets of #8 romex should have been pulled, one feeding each breaker and protected at 60A breakers in the panel. Looking for a consensus since that again may be common practice but seems to not be in line code wise.

Now I think I understand what you are asking. Much was lost in translation. Hopfuly this clearifys and answers your question.
What starts as 2 breakers that are temporarly or perminatly connected so that both trip togeather becomes 1 breaker and that is the only breaker discussed in this thread. When a breaker is installed as part of a furnace it becomes a disconnect.
It is common pratice to have 2 disconnects in an electric furnace/air handler. One supplies only resistance heat strips. The secound supplies all other needs within the furnace AND can supply 1 or more heat strips. The amp rating is not important as long as rating is equal to or greater than load. Local pratice can prohibit this arrangement,but it's normaly approved. A warrning should be displayed on furnace saying it is served by multiple breakers. Wire from breaker box to disconnects and over current protection at breaker box is usualy all that is inspected for compliance with NEC. The 2 breakers nor wire are required to be same amp capacity but each must be sized to it's respective load.
The 2 breakers should be next to one another within the breaker box/load center.