It works more or less now.
At least the remote is now in /proc/bus/input/devices :

I: Bus=0011 Vendor=0001 Product=0001 Version=ab41
N: Name="AT Translated Set 2 keyboard"
P: Phys=isa0060/serio0/input0
S: Sysfs=/class/input/input0
U: Uniq=
H: Handlers=kbd event0
B: EV=120013
B: KEY=84 2044c00 3c12078 f970f409 feffffdf ffefffff ffffffff ffffffff
B: MSC=10
B: LED=7

I: Bus=0019 Vendor=0000 Product=0002 Version=0000
N: Name="Power Button (FF)"
P: Phys=LNXPWRBN/button/input0
S: Sysfs=/class/input/input1
U: Uniq=
H: Handlers=kbd event1
B: EV=3
B: KEY=100000 0 0 0

I: Bus=0019 Vendor=0000 Product=0001 Version=0000
N: Name="Power Button (CM)"
P: Phys=PNP0C0C/button/input0
S: Sysfs=/class/input/input2
U: Uniq=
H: Handlers=kbd event2
B: EV=3
B: KEY=100000 0 0 0

I: Bus=0010 Vendor=001f Product=0001 Version=0100
N: Name="PC Speaker"
P: Phys=isa0061/input0
S: Sysfs=/class/input/input3
U: Uniq=
H: Handlers=kbd event3
B: EV=40001
B: SND=6

I: Bus=0001 Vendor=1421 Product=0350 Version=0001
N: Name="saa7134 IR (ADS Tech Instant TV"
P: Phys=pci-0000:01:06.0/ir0
S: Sysfs=/class/input/input4
U: Uniq=
H: Handlers=kbd event4
B: EV=100003
B: KEY=108c0364 2046 0 0 0 0 2000400 4190 80300801 1e1680 0 10000 40000ffc

I: Bus=0011 Vendor=0002 Product=0005 Version=0000
N: Name="ImPS/2 Generic Wheel Mouse"
P: Phys=isa0060/serio1/input0
S: Sysfs=/class/input/input5
U: Uniq=
H: Handlers=mouse0 event5
B: EV=7
B: KEY=70000 0 0 0 0 0 0 0 0
B: REL=103

I: Bus=0003 Vendor=04ca Product=f001 Version=0001
N: Name="IR-receiver inside an USB DVB receiver"
P: Phys=usb-0000:00:04.1-3/ir0
S: Sysfs=/class/input/input6
U: Uniq=
H: Handlers=kbd event6
B: EV=3
B: KEY=10afcb32 290304b 0 0 0 10004 80018000 180 c0000809 9e16c0 0 0 
10008ffe

( for that last one, i guess my Intuix S800 clone exist with a remote too )

So ...
In the file saa7134-cards.c, add :
    case SAA7134_BOARD_ADS_INSTANT_TV:

Before

        dev->has_remote = SAA7134_REMOTE_GPIO;
        break;
( around line 6659 )
in the file saa7134-input.c, add :
case SAA7134_BOARD_ADS_INSTANT_TV:
        ir_codes = ir_codes_adstech_dvb_t_pci;
        // This remote seems to return 0x7f after each button is pushed.
        // No button may be repeated ; no release message. Only 1 msg with
        // raw data = button idx, followed by one message with raw data 
= 0x7f
        mask_keycode = 0xffffff;
        mask_keyup   = 0xffffff;
        mask_keydown = 0xffffff;
        polling      = 50; // ms
        break;
( around line 654, after "case SAA7134_BOARD_VIDEOMATE_S350:" )

i can use the remote now ( using devinput in lirc ) but a few quirks 
remains :
- dmesg gives a lot of "saa7134 IR (ADS Tech Instant TV: unknown key: 
key=0x7f raw=0x7f down=1"
- in irw most keys are misidentified ( Power as RECORD, Mute as Menu, 
Down as DVD and DVD is correctly identified )

i guess using ir_codes_adstech_dvb_t_pci was not such a bright idea 
after all :p
( i included a full dmesg output )

For now, it is enough work on my part, i'll try to correct those 
keycodes later. It is amazing what you can do even when you don't 
understand most of it :D .