HSI KG 525 PNI non slaved or only slaved? I'm in Germany and currently on a project about the avionics of an older airplane (PA28). Here is a link to a former reddit question.

My Prof. and me want to update the Avionics now - he asked me to do a bit of research - it is quite a good exercise for me and i learn lot this practical way (i'll become an aircraft engineer)!. I do the prework for our maintenance company and they'll supervise my work/planning.   

The main idea is to install new:


Garmin GNS430
Garmin GMA340
Insight G4 + Sensorics
Becker AR6203 22  
KI - 525A or Garmin G5 DG/HSI
Insight G4 for experimental stuff (UAS courses with our piper) 


This avionic stays, but will be reconnected


KN53 (with GS) – goes to KI 204   
KI 204  
KAP 100 (AP)


Will be removed:


GPS150 
KI 203 - Insight G4 will come here instead 
KN53 (w/o GS)
KY 196 (2x COM)


Right now i have the DG - KG107 in it, but my professor wants to update it to a HSI..  


Now the question is if a KI-525A has a built-in gyro or is there only the possibility to connect it with the KG102 (which we dont have)?
I would like to have the new Garmin G5 DG/HSI but it seems that it doesn't have an EASA STC. Garmin is kinda quiet.  What do you think - should we install the G5 (DG/HSI) and hope for a STC or pick another HSI (maybe Century)


EDIT: Took 3 questions off the topic
The G5/430 combination was approved by EASA back in February! No reason why you can't use it. Some advice for you, learning how to use Google search is an invaluable skill for any aircraft engineer. :)