Older versions of Sonar

A lot of the older versions like Sonar 5, 6, 7 and 8.5 cant be purchased anymore.
So im not even sure if you could find these older versions.
 
A few answers are needed first though.(this will help your replied solutions):
- Which version of windows are you running
- what soundcard
- What are your PC specs (the ones that are not good enough to run Sonar Platinum)
 
 

If the new PC is Win 10 and has at least 4GB of RAM it should run Sonar Plat.  How many tracks or MIDI may be an issue but the basic Sonar will run.  I've had Sonar Plat installed on an old 1st generation i5 CPU with 4 GB of RAM and Sonar loaded and ran OK.  I didn't install everything that comes with Platinum, if I used it for on-site recordings it would only be to record up to 8 tracks.  The projects would then be transferred to my desktop DAW for processing. 
 
I now have a new Dell Inspiron 15 (5577) which has a 7th gen i5 and 8GB of RAM.  It passed with flying colors for an on-site recording.  I recorded the complete 3 hour set last week (recorded most of it in 2 song projects) and it worked perfectly.  I used my MOTU 896Mk3 Hybrid recording interface unit.

I don't think the version of Sonar is the issues with underpowered computers. It's possibly more a case of compatibility with audio drivers and OS. Then certain versions were more stable and bug free than others. 
I've used Splat on a very low powered 2008 Sony laptop with 4 gigs Ram. But it has a SSD which is probably important for larger track count. Ram is important if you start adding plug ins and VST's. The processing speed is not as important, it just get things done faster but they'll still get done no matter what.. 
I recorded 16 tracks audio and 1 midi track hours and hours , gig after gig on that machine. 
 
I bought Home Studio to use for this and live playback. It's certainly rock solid no frill and it's way more up to date than if I used 8.5 which now seems a waste of time using to me... I used to love that version.