B9010 sound quality and Yatour CD changer control issues

[C_Hemingway]

CD changer issue:

I have just swapped my radio for a B9010 TNS700 ( Gen5 ? ) Sat Nav unit in my '96 Celica, replacing a 2002 Celica 58806 TNS310 Traffic Plus system as I wanted the colour map display

I also have the Yatour digital CD changer working with it after buying a different cable ( 6+6 instead of 5+7 )

The CD changer module works perfectly in that it will play from the same SD card as was being used with the old 58806 HU and allows the selection of 6 'discs' and use of the track / seek buttons

The 58806 could support 15 'discs' and the Yatour remembered I was listening to Disc13 Track11 even after power interrupt

The B9010 played from this point even up to the last track of Disc15 before wrapping around to Disc1 Track1 all while displaying the correct information at the top of the display

My questions are these: There are only touchscreen buttons for the first 6 discs but is there a disc up / disc down option to manually cycle through Discs?

How many 'discs' can the B9010 handle with the Yatour module?

Sound quality issue:

I am using the standard '96 Celica GT 4-speaker setup which sounded great with the 58806 and the original stereo/cassette, all of which are internally amplified

With the B9010, even with the Bass and Mid-level set to max, everything still sounds a little 'tinny'

The Sat Nav voice on the TNS310, I think might also have been controlled by the HU bass / treble, was strong and clear but with the B9010 now sounds extremely tinny but I can't find any way of controlling this sound output

I'm not one to drive around with my 'boom-boom' music, but I do like a good level of bass ( max bass without aftermarket amplifier has always been good enough for me )

Is there a way of improving this without adding an external amplifier?