As an R5 owner, the bank-link scan feature alone makes it a worthy upgrade. Imagine if all the handhelds you owned only allowed you to scan one bank at a time, or every single one, but no combination of banks that you want.
I hate to play the specs game, but it appears that there is a bit more selectivity. For airband monitoring, every little bit helps, as most filters are too wide for higher-quality airband am comms.
The AF filter (lowpass probably) helps yet again for airband. HF too, but I never use this for HF.
VSC - voice squelch - works ok and helps when monitoring a channel that has a carrier on it, like from your dsl box, etc. Not a perfect solution, but it helps when the system isn't using pl. Not useful when scanning as it slows down the scan rate to evaluate the signal, but for single-channel monitoring, pretty neat when it works. Nice on the RX-7 for sure for me.
About 100 more memory channels, but the big news is that on the R5, there were about 8 alpha banks that were reserved for the system, whereas it looks like this limit has been reduced in half to 4 reservations for the R6.
CI-V data link for those that need that kind of interconnectivity and control.
Backlight option now includes permanent on state when used from external dc supply.
Charger now has a "trickle" option in addition to the standard 15 hour timer for the spec 1400 / 1500 mah batts. I suppose this would be very handy to get those 2000 mah eneloops charged properly with an additional hour or two of trickling, rather than resetting the 15 hour timer and keeping an eagle-eye on it as you force another charge cycle. Also seems to have a bad-battery detector (ie won't take a charge, so you don't end up charging just one of the two required). Emphasis on NIMH with warnings about NOT using nicads or li-on rechargeables.
Then again, most of us probably just buy new AA's, or recharge outside the unit.
And still no REAL narrow-fm as defined by today's standard. C'mon Icom, do a last-minute surprise!
AND still a mono headphone jack! I don't know about anyone else, but a single-earpiece does not cut it under "noisy conditions". I have to carry around this mono-stereo adapter kluge that gets right in the way for using any form of stereo headset (yes, only mono, but I need mono in BOTH ears) that is now used in 99.999% of the world. The AF filter will do wonders to make the typical hi-fi earbuds at least tolerable with the R6 for communications use.
The big issue is how does it sound? If the audio is poor, then none of the above matters. I'm hoping it at least equals or even exceeds the R5. In fact, with today's battery capacity, I was hoping for even more audio output, but I guess we'll see.
